-
-
Notifications
You must be signed in to change notification settings - Fork 1.1k
/
Copy pathmigration-schema.html
58 lines (56 loc) · 87.5 KB
/
migration-schema.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
<!doctype html>
<html lang="en" dir="ltr" class="docs-wrapper plugin-docs plugin-id-default docs-version-current docs-doc-page docs-doc-id-migration-schema" data-has-hydrated="false">
<head>
<meta charset="UTF-8">
<meta name="generator" content="Docusaurus v3.7.0">
<title data-rh="true">Seamless Schema Data Migration with RxDB | RxDB - JavaScript Database</title><meta data-rh="true" name="viewport" content="width=device-width,initial-scale=1"><meta data-rh="true" name="twitter:card" content="summary_large_image"><meta data-rh="true" property="og:image" content="https://rxdb.info/img/rxdb_social_card.png"><meta data-rh="true" name="twitter:image" content="https://rxdb.info/img/rxdb_social_card.png"><meta data-rh="true" property="og:url" content="https://rxdb.info/migration-schema.html"><meta data-rh="true" property="og:locale" content="en"><meta data-rh="true" name="docusaurus_locale" content="en"><meta data-rh="true" name="docsearch:language" content="en"><meta data-rh="true" name="docusaurus_version" content="current"><meta data-rh="true" name="docusaurus_tag" content="docs-default-current"><meta data-rh="true" name="docsearch:version" content="current"><meta data-rh="true" name="docsearch:docusaurus_tag" content="docs-default-current"><meta data-rh="true" property="og:title" content="Seamless Schema Data Migration with RxDB | RxDB - JavaScript Database"><meta data-rh="true" name="description" content="Upgrade your RxDB collections without losing data. Learn how to seamlessly migrate schema changes and keep your apps running smoothly."><meta data-rh="true" property="og:description" content="Upgrade your RxDB collections without losing data. Learn how to seamlessly migrate schema changes and keep your apps running smoothly."><link data-rh="true" rel="icon" href="/img/favicon.ico"><link data-rh="true" rel="canonical" href="https://rxdb.info/migration-schema.html"><link data-rh="true" rel="alternate" href="https://rxdb.info/migration-schema.html" hreflang="en"><link data-rh="true" rel="alternate" href="https://rxdb.info/migration-schema.html" hreflang="x-default"><link rel="preconnect" href="https://www.google-analytics.com">
<link rel="preconnect" href="https://www.googletagmanager.com">
<script async src="https://www.googletagmanager.com/gtag/js?id=G-62D63SY3S0"></script>
<script>function gtag(){dataLayer.push(arguments)}window.dataLayer=window.dataLayer||[],gtag("js",new Date),gtag("config","G-62D63SY3S0",{})</script>
<link rel="preconnect" href="https://www.googletagmanager.com">
<script>window.dataLayer=window.dataLayer||[]</script>
<script>!function(e,t,a,n){e[n]=e[n]||[],e[n].push({"gtm.start":(new Date).getTime(),event:"gtm.js"});var g=t.getElementsByTagName(a)[0],m=t.createElement(a);m.async=!0,m.src="https://www.googletagmanager.com/gtm.js?id=GTM-PL63TR5",g.parentNode.insertBefore(m,g)}(window,document,"script","dataLayer")</script><link rel="stylesheet" href="/assets/css/styles.bc483400.css">
<script src="/assets/js/runtime~main.68ae4ffa.js" defer="defer"></script>
<script src="/assets/js/main.90e814da.js" defer="defer"></script>
</head>
<body class="navigation-with-keyboard">
<noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-PL63TR5" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
<script>!function(){function t(t){document.documentElement.setAttribute("data-theme",t)}var e=function(){try{return new URLSearchParams(window.location.search).get("docusaurus-theme")}catch(t){}}()||function(){try{return window.localStorage.getItem("theme")}catch(t){}}();t(null!==e?e:"dark")}(),function(){try{const n=new URLSearchParams(window.location.search).entries();for(var[t,e]of n)if(t.startsWith("docusaurus-data-")){var a=t.replace("docusaurus-data-","data-");document.documentElement.setAttribute(a,e)}}catch(t){}}()</script><div id="__docusaurus"><div role="region" aria-label="Skip to main content"><a class="skipToContent_fXgn" href="#__docusaurus_skipToContent_fallback">Skip to main content</a></div><nav aria-label="Main" class="navbar navbar--fixed-top"><div class="navbar__inner"><div class="navbar__items"><button aria-label="Toggle navigation bar" aria-expanded="false" class="navbar__toggle clean-btn" type="button"><svg width="30" height="30" viewBox="0 0 30 30" aria-hidden="true"><path stroke="currentColor" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2" d="M4 7h22M4 15h22M4 23h22"></path></svg></button><a class="navbar__brand" href="/"><div class="navbar__logo"><img src="/files/logo/logo.svg" alt="RxDB Logo" class="themedComponent_mlkZ themedComponent--light_NVdE"><img src="/files/logo/logo.svg" alt="RxDB Logo" class="themedComponent_mlkZ themedComponent--dark_xIcU"></div><b class="navbar__title text--truncate">RxDB</b></a></div><div class="navbar__items navbar__items--right"><a class="navbar__item navbar__link" href="/consulting/">Support</a><a class="navbar__item navbar__link" href="/premium/">Premium</a><a class="navbar__item navbar__link" href="/overview.html">Docs</a><div class="navbarSearchContainer_Bca1"></div></div></div><div role="presentation" class="navbar-sidebar__backdrop"></div></nav><div style="position:fixed;display:block;z-index:10;height:1.5px;background-color:var(--color-top);top:62.5px;border-top-right-radius:2px;border-bottom-right-radius:2px;width:0%"></div><div id="__docusaurus_skipToContent_fallback" class="main-wrapper mainWrapper_z2l0"><div class="docsWrapper_hBAB"><button aria-label="Scroll back to top" class="clean-btn theme-back-to-top-button backToTopButton_sjWU" type="button"></button><div class="docRoot_UBD9"><aside class="theme-doc-sidebar-container docSidebarContainer_YfHR"><div class="sidebarViewport_aRkj"><div class="sidebar_njMd"><nav aria-label="Docs sidebar" class="menu thin-scrollbar menu_SIkG"><ul class="theme-doc-sidebar-menu menu__list"><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="true" href="/overview.html">Getting Started with RxDB</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/overview.html">Overview</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/quickstart.html">🚀 Quickstart</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/install.html">Installation</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/dev-mode.html">Development Mode</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/tutorials/typescript.html">TypeScript Setup</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="true" href="/rx-database.html">Core Entities</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-database.html">RxDatabase</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-schema.html">RxSchema</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-collection.html">RxCollection</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-document.html">RxDocument</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-query.html">RxQuery</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/rx-storage.html">💾 Storages</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/schema-validation.html">Storage Wrappers</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/replication.html">🔄 Replication</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/rx-server.html">Server</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/transactions-conflicts-revisions.html">How RxDB works</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" role="button" aria-expanded="true" href="/migration-schema.html">Advanced Features</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-2 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" role="button" aria-expanded="true" tabindex="0" href="/migration-schema.html">Migration</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="/migration-schema.html">Schema Migration</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-3 menu__list-item"><a class="menu__link" tabindex="0" href="/migration-storage.html">Storage Migration</a></li></ul></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-attachment.html">Attachments</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-pipeline.html">RxPipelines</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/reactivity.html">Custom Reactivity</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-state.html">RxState</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/rx-local-document.html">Local Documents</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/cleanup.html">Cleanup</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/backup.html">Backup</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/leader-election.html">Leader Election</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/middleware.html">Middleware</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/crdt.html">CRDT</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/population.html">Population</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/orm.html">ORM</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/fulltext-search.html">Fulltext Search 👑</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/articles/javascript-vector-database.html">Vector Database</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/query-optimizer.html">Query Optimizer 👑</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/third-party-plugins.html">Third Party Plugins</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/rx-storage-performance.html">Performance</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/releases/16.0.0.html">Releases</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/offline-first.html">Articles</a></div></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="/contribution.html">Contribute & Innovate with RxDB</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" role="button" aria-expanded="false" href="/consulting/">Contact</a></div></li></ul></nav></div></div></aside><main class="docMainContainer_TBSr"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label="Breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="/"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Advanced Features</span><meta itemprop="position" content="1"></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Migration</span><meta itemprop="position" content="2"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Schema Migration</span><meta itemprop="position" content="3"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Migrate Database Data on schema changes</h1></header>
<p>The RxDB Data Migration Plugin helps developers easily update stored data in their apps when they make changes to the data structure by changing the schema of a <a href="/rx-collection.html">RxCollection</a>. This is useful when developers release a new version of the app with a different schema.</p>
<p>Imagine you have your awesome messenger-app distributed to many users. After a while, you decide that in your new version, you want to change the schema of the messages-collection. Instead of saving the message-date like <code>2017-02-12T23:03:05+00:00</code> you want to have the unix-timestamp like <code>1486940585</code> to make it easier to compare dates. To accomplish this, you change the schema and <strong>increase the version-number</strong> and you also change your code where you save the incoming messages. But one problem remains: what happens with the messages which are already stored in the database on the user's device in the old schema?</p>
<p>With RxDB you can provide migrationStrategies for your collections that automatically (or on call) transform your existing data from older to newer schemas. This assures that the client's data always matches your newest code-version.</p>
<h1>Add the migration plugin</h1>
<p>To enable the data migration, you have to add the <code>migration-schema</code> plugin.</p>
<div class="language-ts codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-ts codeBlock_bY9V thin-scrollbar" style="color:#F8F8F2;background-color:#282A36"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">import</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"> addRxPlugin </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">from</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">'rxdb'</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">import</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"> RxDBMigrationSchemaPlugin </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">from</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">'rxdb/plugins/migration-schema'</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token function" style="color:rgb(80, 250, 123)">addRxPlugin</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">RxDBMigrationSchemaPlugin</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="providing-strategies">Providing strategies<a href="#providing-strategies" class="hash-link" aria-label="Direct link to Providing strategies" title="Direct link to Providing strategies"></a></h2>
<p>Upon creation of a collection, you have to provide migrationStrategies when your schema's version-number is greater than <code>0</code>. To do this, you have to add an object to the <code>migrationStrategies</code> property where a function for every schema-version is assigned. A migrationStrategy is a function which gets the old document-data as a parameter and returns the new, transformed document-data. If the strategy returns <code>null</code>, the document will be removed instead of migrated.</p>
<div class="language-javascript codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-javascript codeBlock_bY9V thin-scrollbar" style="color:#F8F8F2;background-color:#282A36"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token plain">myDatabase</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">addCollections</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">messages</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">schema</span><span class="token operator">:</span><span class="token plain"> messageSchemaV1</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">migrationStrategies</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// 1 means, this transforms data from version 0 to version 1</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">1</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">time</span><span class="token plain"> </span><span class="token operator">=</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">new</span><span class="token plain"> </span><span class="token class-name">Date</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">time</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">getTime</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// string to unix</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<p>Asynchronous strategies can also be used:</p>
<div class="language-javascript codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-javascript codeBlock_bY9V thin-scrollbar" style="color:#F8F8F2;background-color:#282A36"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token plain">myDatabase</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">addCollections</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">messages</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">schema</span><span class="token operator">:</span><span class="token plain"> messageSchemaV1</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">migrationStrategies</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">1</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">time</span><span class="token plain"> </span><span class="token operator">=</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">new</span><span class="token plain"> </span><span class="token class-name">Date</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">time</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">getTime</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// string to unix</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token doc-comment comment" style="color:rgb(98, 114, 164)">/**</span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token doc-comment comment" style="color:rgb(98, 114, 164)"> * 2 means, this transforms data from version 1 to version 2</span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token doc-comment comment" style="color:rgb(98, 114, 164)"> * this returns a promise which resolves with the new document-data</span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token doc-comment comment" style="color:rgb(98, 114, 164)"> */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">2</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// in the new schema (version: 2) we defined 'senderCountry' as required field (string)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// so we must get the country of the message-sender from the server</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">const</span><span class="token plain"> coordinates </span><span class="token operator">=</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">coordinates</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> </span><span class="token function" style="color:rgb(80, 250, 123)">fetch</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">'http://myserver.com/api/countryByCoordinates/'</span><span class="token operator">+</span><span class="token plain">coordinates</span><span class="token operator">+</span><span class="token string" style="color:rgb(255, 121, 198)">'/'</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">then</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">response</span><span class="token plain"> </span><span class="token arrow operator">=></span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">const</span><span class="token plain"> response </span><span class="token operator">=</span><span class="token plain"> response</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">json</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">senderCountry</span><span class="token plain"> </span><span class="token operator">=</span><span class="token plain"> response</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<p>you can also filter which documents should be migrated:</p>
<div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar" style="color:#F8F8F2;background-color:#282A36"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token plain">myDatabase</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">addCollections</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">messages</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">schema</span><span class="token operator">:</span><span class="token plain"> messageSchemaV1</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">migrationStrategies</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// 1 means, this transforms data from version 0 to version 1</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">1</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">time</span><span class="token plain"> </span><span class="token operator">=</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">new</span><span class="token plain"> </span><span class="token class-name">Date</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">time</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">getTime</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// string to unix</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token doc-comment comment" style="color:rgb(98, 114, 164)">/**</span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token doc-comment comment" style="color:rgb(98, 114, 164)"> * this removes all documents older then 2017-02-12</span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token doc-comment comment" style="color:rgb(98, 114, 164)"> * they will not appear in the new collection</span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token doc-comment comment" style="color:rgb(98, 114, 164)"> */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">2</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">time</span><span class="token plain"> </span><span class="token operator"><</span><span class="token plain"> </span><span class="token number">1486940585</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> </span><span class="token keyword null nil" style="color:rgb(189, 147, 249);font-style:italic">null</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">else</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="automigrate">autoMigrate<a href="#automigrate" class="hash-link" aria-label="Direct link to autoMigrate" title="Direct link to autoMigrate"> </a></h2>
<p>By default, the migration automatically happens when the collection is created. Calling <code>RxDatabase.addCollections()</code> returns only when the migration has finished.
If you have lots of data or the migrationStrategies take a long time, it might be better to start the migration 'by hand' and show the migration-state to the user as a loading-bar.</p>
<div class="language-javascript codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-javascript codeBlock_bY9V thin-scrollbar" style="color:#F8F8F2;background-color:#282A36"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">const</span><span class="token plain"> messageCol </span><span class="token operator">=</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">await</span><span class="token plain"> myDatabase</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">addCollections</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">messages</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">schema</span><span class="token operator">:</span><span class="token plain"> messageSchemaV1</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">autoMigrate</span><span class="token operator">:</span><span class="token plain"> </span><span class="token boolean">false</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// <- migration will not run at creation</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">migrationStrategies</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">1</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">async</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token spread operator">...</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> anything that takes very long</span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token spread operator">...</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// check if migration is needed</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">const</span><span class="token plain"> needed </span><span class="token operator">=</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">await</span><span class="token plain"> messageCol</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">migrationNeeded</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">if</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">needed </span><span class="token operator">==</span><span class="token plain"> </span><span class="token boolean">false</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// start the migration</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">messageCol</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">startMigration</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token number">10</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// 10 is the batch-size, how many docs will run at parallel</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">const</span><span class="token plain"> migrationState </span><span class="token operator">=</span><span class="token plain"> messageCol</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">getMigrationState</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// 'start' the observable</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">migrationState</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">$</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">subscribe</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token function-variable function" style="color:rgb(80, 250, 123)">next</span><span class="token operator">:</span><span class="token plain"> </span><span class="token parameter">state</span><span class="token plain"> </span><span class="token arrow operator">=></span><span class="token plain"> </span><span class="token console class-name">console</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">dir</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">state</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token function-variable function" style="color:rgb(80, 250, 123)">error</span><span class="token operator">:</span><span class="token plain"> </span><span class="token parameter">error</span><span class="token plain"> </span><span class="token arrow operator">=></span><span class="token plain"> </span><span class="token console class-name">console</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">error</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">error</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token function-variable function" style="color:rgb(80, 250, 123)">complete</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token arrow operator">=></span><span class="token plain"> </span><span class="token console class-name">console</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">'done'</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// the emitted states look like this:</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">status</span><span class="token operator">:</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">'RUNNING'</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// oneOf 'RUNNING' | 'DONE' | 'ERROR'</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">count</span><span class="token operator">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">total</span><span class="token operator">:</span><span class="token plain"> </span><span class="token number">50</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// amount of documents which must be migrated</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">handled</span><span class="token operator">:</span><span class="token plain"> </span><span class="token number">0</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// amount of handled docs</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token literal-property property">percent</span><span class="token operator">:</span><span class="token plain"> </span><span class="token number">0</span><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// percentage [0-100]</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<p>If you don't want to show the state to the user, you can also use <code>.migratePromise()</code>:</p>
<div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar" style="color:#F8F8F2;background-color:#282A36"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">const</span><span class="token plain"> migrationPromise </span><span class="token operator">=</span><span class="token plain"> messageCol</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">migratePromise</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token number">10</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">await</span><span class="token plain"> migratePromise</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="migrationstates">migrationStates()<a href="#migrationstates" class="hash-link" aria-label="Direct link to migrationStates()" title="Direct link to migrationStates()"></a></h2>
<p><code>RxDatabase.migrationStates()</code> returns an <code>Observable</code> that emits all migration states of any collection of the database.
Use this when you add collections dynamically and want to show a loading-state of the migrations to the user.</p>
<div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar" style="color:#F8F8F2;background-color:#282A36"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">const</span><span class="token plain"> allStatesObservable </span><span class="token operator">=</span><span class="token plain"> myDatabase</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">migrationStates</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">allStatesObservable</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">subscribe</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">allStates</span><span class="token plain"> </span><span class="token arrow operator">=></span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> allStates</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">forEach</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">migrationState</span><span class="token plain"> </span><span class="token arrow operator">=></span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token console class-name">console</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token method function property-access" style="color:rgb(80, 250, 123)">log</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">'migration state of '</span><span class="token plain"> </span><span class="token operator">+</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> migrationState</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">collection</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">name</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="migrating-attachments">Migrating attachments<a href="#migrating-attachments" class="hash-link" aria-label="Direct link to Migrating attachments" title="Direct link to Migrating attachments"></a></h2>
<p>When you store <code>RxAttachment</code>s together with your document, they can also be changed, added or removed while running the migration.
You can do this by mutating the <code>oldDoc._attachments</code> property.</p>
<div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar" style="color:#F8F8F2;background-color:#282A36"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword module" style="color:rgb(189, 147, 249);font-style:italic">import</span><span class="token plain"> </span><span class="token imports punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token imports"> createBlob </span><span class="token imports punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"> </span><span class="token keyword module" style="color:rgb(189, 147, 249);font-style:italic">from</span><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">'rxdb'</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">const</span><span class="token plain"> migrationStrategies </span><span class="token operator">=</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">1</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">async</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// do nothing with _attachments to keep all attachments and have them in the new collection version.</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">2</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">async</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// set _attachments to an empty object to delete all existing ones during the migration.</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">_attachments</span><span class="token plain"> </span><span class="token operator">=</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token number">3</span><span class="token operator">:</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">async</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">function</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token parameter">oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token comment" style="color:rgb(98, 114, 164)">// update the data field of a single attachment to change its data. </span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">_attachments</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">myFile</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">data</span><span class="token plain"> </span><span class="token operator">=</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">await</span><span class="token plain"> </span><span class="token function" style="color:rgb(80, 250, 123)">createBlob</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token string" style="color:rgb(255, 121, 198)">'my new text'</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">_attachments</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">myFile</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token property-access">content_type</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword control-flow" style="color:rgb(189, 147, 249);font-style:italic">return</span><span class="token plain"> oldDoc</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="migration-on-multi-tab-in-browsers">Migration on multi-tab in browsers<a href="#migration-on-multi-tab-in-browsers" class="hash-link" aria-label="Direct link to Migration on multi-tab in browsers" title="Direct link to Migration on multi-tab in browsers"></a></h2>
<p>If you use RxDB in a multiInstance environment, like a browser, it will ensure that exactly one tab is running a migration of a collection.
Also the <code>migrationState.$</code> events are emitted between browser tabs.</p>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="migration-and-replication">Migration and Replication<a href="#migration-and-replication" class="hash-link" aria-label="Direct link to Migration and Replication" title="Direct link to Migration and Replication"></a></h2>
<p>If you use any of the <a href="/replication.html">RxReplication</a> plugins, the migration will also run on the internal replication-state storage. It will migrate all <code>assumedMasterState</code> documents
so that after the migration is done, you do not have to re-run the replication from scratch.
RxDB assumes that you run the exact same migration on the servers and the clients. Notice that the replication <code>pull-checkpoint</code> will not be migrated. Your backend must be compatible with pull-checkpoints of older versions.</p>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id="migration-should-be-run-on-all-database-instances">Migration should be run on all database instances<a href="#migration-should-be-run-on-all-database-instances" class="hash-link" aria-label="Direct link to Migration should be run on all database instances" title="Direct link to Migration should be run on all database instances"></a></h2>
<p>If you have multiple database instances (for example, if you are running replication inside of a <a href="/rx-storage-worker.html">Worker</a> or <a href="/rx-storage-shared-worker.html">SharedWorker</a> and have created a database instance inside of the worker), schema migration should be started on all database instances. All instances must know about all migration strategies and any updated schema versions.</p></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"><a class="pagination-nav__link pagination-nav__link--prev" href="/errors.html"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Errors</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/migration-storage.html"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">Storage Migration</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#providing-strategies" class="table-of-contents__link toc-highlight">Providing strategies</a></li><li><a href="#automigrate" class="table-of-contents__link toc-highlight">autoMigrate</a></li><li><a href="#migrationstates" class="table-of-contents__link toc-highlight">migrationStates()</a></li><li><a href="#migrating-attachments" class="table-of-contents__link toc-highlight">Migrating attachments</a></li><li><a href="#migration-on-multi-tab-in-browsers" class="table-of-contents__link toc-highlight">Migration on multi-tab in browsers</a></li><li><a href="#migration-and-replication" class="table-of-contents__link toc-highlight">Migration and Replication</a></li><li><a href="#migration-should-be-run-on-all-database-instances" class="table-of-contents__link toc-highlight">Migration should be run on all database instances</a></li></ul></div></div></div></div></main></div></div></div><div class="block footer"><div class="footer-block"><div class="footer-links"><span><a variant="text" href="/" class="footer-logo-button"><img src="/files/logo/logo.svg" alt="RxDB" loading="lazy"><div>RxDB</div></a><div class="footer-community-links"><a variant="text" href="/chat/" target="_blank"><img src="/img/community-links/discord-logo.svg" alt="RxDB Discord" loading="lazy"></a><a variant="text" href="/code/" target="_blank"><img src="/img/community-links/github-logo.svg" alt="RxDB Github" loading="lazy"></a><a variant="text" href="https://twitter.com/intent/user?screen_name=rxdbjs" target="_blank"><img src="/img/community-links/x-logo.svg" alt="RxDB Twitter" loading="lazy"></a><a variant="text" href="https://www.linkedin.com/company/rxdb" target="_blank"><img src="/img/community-links/linkedin-logo.svg" alt="RxDB LinkedIn" loading="lazy"></a><a variant="text" href="https://stackoverflow.com/questions/tagged/rxdb" target="_blank"><img src="/img/community-links/stack-overflow-logo.svg" alt="RxDB Stack Overflow" loading="lazy"></a></div></span><div class="footer-nav-links"><a variant="text" href="/premium/" target="">Premium</a><a variant="text" href="/consulting/" target="">Support</a><a variant="text" href="/overview.html" target="">Documentation</a><a variant="text" href="/chat/" target="_blank">Discord</a><a variant="text" href="/code/" target="_blank">Github</a><a variant="text" href="https://twitter.com/intent/user?screen_name=rxdbjs" target="_blank">Twitter</a><a variant="text" href="https://www.linkedin.com/company/rxdb" target="_blank">LinkedIn</a></div></div><div class="footer-policy"><div><a variant="text" href="/legal-notice/" target="_blank">Legal Notice</a></div><span class="footer-rights">© 2025 RxDB. All rights reserved.</span></div><img class="footer-img desktop-img" src="/img/footer-column.svg" alt="columns" loading="lazy"></div></div><div class="call-to-action-popup"><div class="close"><div class="text">✕</div></div></div></div>
</body>
</html>