react-native-onyx

Persistent storage solution wrapped in a Pub/Sub library.

Features

• Onyx stores and retrieves data from persistent storage
• Data is stored as key/value pairs, where the value can be anything from a single piece of data to a complex object
• Collections of data are usually not stored as a single key (e.g. an array with multiple objects), but as individual keys+ID (e.g. report_1234, report_4567, etc.). Store collections as individual keys when a component will bind directly to one of those keys. For example: reports are stored as individual keys because SidebarLink.js binds to the individual report keys for each link. However, report actions are stored as an array of objects because nothing binds directly to a single report action.
• Onyx allows other code to subscribe to changes in data, and then publishes change events whenever data is changed
• Anything needing to read Onyx data needs to:
  1. Know what key the data is stored in (for web, you can find this by looking in the JS console > Application > local storage)
  2. Subscribe to changes of the data for a particular key or set of keys. React components use withOnyx() and non-React libs use Onyx.connect().
  3. Get initialized with the current value of that key from persistent storage (Onyx does this by calling setState() or triggering the callback with the values currently on disk as part of the connection process)
• Subscribing to Onyx keys is done using a constant defined in ONYXKEYS. Each Onyx key represents either a collection of items or a specific entry in storage. For example, since all reports are stored as individual keys like report_1234, if code needs to know about all the reports (e.g. display a list of them in the nav menu), then it would subscribe to the key ONYXKEYS.COLLECTION.REPORT.

Getting Started

Installation

Onyx is published to npm

npm install react-native-onyx --save

Initialization

To initialize Onyx we call Onyx.init() with a configuration object.

import Onyx from 'react-native-onyx';

const ONYXKEYS = {
    SESSION: 'session',
};

const config = {
    keys: ONYXKEYS,
};

Onyx.init(config);

Usage in non react-native projects

Onyx can be used in non react-native projects, by leveraging the browser field in package.json Bundlers like Webpack respect that field and import code from the specified path We import Onyx the same way shown above - import Onyx from 'react-native-onyx'

Setting data

To store some data we can use the Onyx.set() method.

API.Authenticate(params)
    .then((response) => {
        Onyx.set(ONYXKEYS.SESSION, {token: response.token});
    });

The data will then be cached and stored via AsyncStorage.

Merging data

We can also use Onyx.merge() to merge new Object or Array data in with existing data.

For Array the default behavior is to replace it fully, effectively making it equivalent to set:

Onyx.merge(ONYXKEYS.EMPLOYEE_LIST, ['Joe']); // -> ['Joe']
Onyx.merge(ONYXKEYS.EMPLOYEE_LIST, ['Jack']); // -> ['Joe', 'Jack']

For Object values the default behavior uses lodash/merge under the hood to do a deep extend of the object.

Onyx.merge(ONYXKEYS.POLICY, {id: 1}); // -> {id: 1}
Onyx.merge(ONYXKEYS.POLICY, {name: 'My Workspace'}); // -> {id: 1, name: 'My Workspace'}

Arrays inside objects will be replaced fully, same as arrays not inside objects:

Onyx.merge(ONYXKEYS.POLICY, {employeeList: ['Joe', 'Jack']}); // -> {employeeList: ['Joe', 'Jack']}
Onyx.merge(ONYXKEYS.POLICY, {employeeList: ['Jack']}); // -> {employeeList: ['Jack']}

Should I use merge() or set() or both?

• Use merge() when creating a new object
• Use merge() to merge partial data into an existing object
• Use merge() when storing simple values (String, Boolean, Number)
• Use set() when you need to delete an Onyx key completely from storage
• Use set() when you need to completely reset an object or array of data

Consecutive calls to Onyx.merge() with the same key are batched in a stack and processed in the order that they were called. This helps avoid race conditions where one merge possibly finishes before another. However, it's important to note that calls to Onyx.set() are not batched together with calls to Onyx.merge(). For this reason, it is usually preferable to use one or the other, but not both. Onyx is a work-in-progress so always test code to make sure assumptions are correct!

Should I store things as an array or an object?

You should avoid arrays as much as possible. They do not work well with merge() because it can't update a single element in an array, it must always set the entire array each time. This forces you to use set() a lot, and as seen above, merge() is more performant and better to use in almost any situation. If you are working with an array of objects, then you should be using an Onyx collection because it's optimized for working with arrays of objects.

Subscribing to data changes

To set up a basic subscription for a given key use the Onyx.connect() method.

let session;
const connectionID = Onyx.connect({
    key: ONYXKEYS.SESSION,
    callback: (val) => session = val || {},
});

To teardown the subscription call Onyx.disconnect() with the connectionID returned from Onyx.connect(). It's recommended to clean up subscriptions anytime you are connecting from within a function to prevent memory leaks.

Onyx.disconnect(connectionID);

We can also access values inside React components via the withOnyx() higher order component. When the data changes the component will re-render.

import React from 'react';
import {withOnyx} from 'react-native-onyx';

const App = ({session}) => (
    <View>
        {session.token ? <Text>Logged in</Text> : <Text>Logged out</Text> }
    </View>
);

export default withOnyx({
    session: {
        key: ONYXKEYS.SESSION,
    },
})(App);

It is preferable to use the HOC over Onyx.connect() in React code as withOnyx() will delay the rendering of the wrapped component until all keys have been accessed and made available.

Collections

Collections allow keys with similar value types to be subscribed together by subscribing to the collection key. To define one, it must be included in the ONYXKEYS.COLLECTION object and it must be suffixed with an underscore. Member keys should use a unique identifier or index after the collection key prefix (e.g. report_42).

const ONYXKEYS = {
    COLLECTION: {
        REPORT: 'report_',
    },
};

Setting Collection Values

To save a new collection key we can either do:

Onyx.merge(`${ONYXKEYS.COLLECTION.REPORT}${report1.reportID}`, report1);

or we can set many at once with mergeCollection() (see below for guidance on best practices):

Onyx.mergeCollection(ONYXKEYS.COLLECTION.REPORT, {
    [`${ONYXKEYS.COLLECTION.REPORT}${report1.reportID}`]: report1,
    [`${ONYXKEYS.COLLECTION.REPORT}${report2.reportID}`]: report2,
    [`${ONYXKEYS.COLLECTION.REPORT}${report3.reportID}`]: report3,
});

Subscribing to Collections

There are several ways to subscribe to these keys:

withOnyx({
    allReports: {key: ONYXKEYS.COLLECTION.REPORT},
})(MyComponent);

This will add a prop to the component called allReports which is an object of collection member key/values. Changes to the individual member keys will modify the entire object and new props will be passed with each individual key update. The prop doesn't update on the initial rendering of the component until the entire collection has been read out of Onyx.

Onyx.connect({key: ONYXKEYS.COLLECTION.REPORT}, callback: (memberValue, memberKey) => {...}});

This will fire the callback once per member key depending on how many collection member keys are currently stored. Changes to those keys after the initial callbacks fire will occur when each individual key is updated.

Onyx.connect({
    key: ONYXKEYS.COLLECTION.REPORT,
    waitForCollectionCallback: true,
    callback: (allReports) => {...}},
});

This final option forces Onyx.connect() to behave more like withOnyx() and only update the callback once with the entire collection initially and later with an updated version of the collection when individual keys update.

Performance Considerations When Using Collections

Be cautious when using collections as things can get out of hand if you have a subscriber hooked up to a collection key that has large numbers of individual keys. If this is the case, it is critical to use mergeCollection() over merge().

Remember, mergeCollection() will notify a subscriber only once with the total collected values whereas each call to merge() would re-render a connected component each time it is called. Consider this example where reports is an array of reports that we want to index and save.

// Bad
_.each(reports, report => Onyx.merge(`${ONYXKEYS.COLLECTION.REPORT}${report.reportID}`, report)); // -> A component using withOnyx() will have it's state updated with each iteration

// Good
const values = {};
_.each(reports, report => values[`${ONYXKEYS.COLLECTION.REPORT}${report.reportID}`] = report);
Onyx.mergeCollection(ONYXKEYS.COLLECTION.REPORT, values); // -> A component using withOnyx() will only have it's state updated once

Clean up

To clear all data from Onyx we can use Onyx.clear().

function signOut() {
    Onyx.clear();
}

Storage Providers

Onyx.get/set and the rest of the API accesses the underlying storage differently depending on the platform

Under the hood storage access calls are delegated to a StorageProvider Some platforms (like web and desktop) might use the same storage provider

If a platform needs to use a separate library (like using MMVK for react-native) it should be added in the following way:

1. Create a StorageProvider.js at lib/storage/providers Reference an existing StorageProvider for the interface that has to be implemented
2. Update the factory at lib/storage/index.web.js and lib/storage/index.native.js to return the newly created Provider for the desired Platform(s)

API Reference

Docs

Storage Eviction

Different platforms come with varying storage capacities and Onyx has a way to gracefully fail when those storage limits are encountered. When Onyx fails to set or modify a key the following steps are taken:

1. Onyx looks at a list of recently accessed keys (access is defined as subscribed to or modified) and locates the key that was least recently accessed
2. It then deletes this key and retries the original operation

By default, Onyx will not evict anything from storage and will presume all keys are "unsafe" to remove unless explicitly told otherwise.

To flag a key as safe for removal:

• Add the key to the safeEvictionKeys option in Onyx.init(options)
• Implement canEvict in the Onyx config for each component subscribing to a key
• The key will only be deleted when all subscribers return true for canEvict

e.g.

Onyx.init({
    safeEvictionKeys: [ONYXKEYS.COLLECTION.REPORT_ACTIONS],
});

export default withOnyx({
    reportActions: {
        key: ({reportID}) => `${ONYXKEYS.COLLECTION.REPORT_ACTIONS}${reportID}_`,
        canEvict: props => !props.isActiveReport,
    },
})(ReportActionsView);

Benchmarks

Provide the captureMetrics boolean flag to Onyx.init to capture call statistics

Onyx.init({
    keys: ONYXKEYS,
    safeEvictionKeys: [ONYXKEYS.COLLECTION.REPORT_ACTIONS],
    captureMetrics: Config.BENCHMARK_ONYX,
});

At any point you can get the collected statistics using Onyx.getMetrics(). This will return an object containing totalTime, averageTime and summaries. summaries is a collection of statistics for each method it contains data about:

• method name
• total, max, min, average times for this method calls
• calls - a list of individual calls with each having: start time; end time; call duration; call arguments
  • start/end times are relative to application launch time - 0.00 being exactly at launch

If you wish to reset the metrics and start over use Onyx.resetMetrics()

Finally, there's a Onyx.printMetrics() method which prints human statistics information on the dev console. You can use this method during debugging. For example add an Onyx.printMetrics() line somewhere in code or call it through the dev console. It supports 3 popular formats MD - human friendly markdown, CSV and JSON. The default is MD if you want to print another format call Onyx.printMetrics({ format: 'csv' }) or Onyx.printMetrics({ format: 'json' }).

Sample output of Onyx.printMetrics()

### Onyx Benchmark
  - Total: 1.5min
  - Last call finished at: 12.55sec

|     method      | total time spent |    max    |   min    |    avg    | time last call completed | calls made |
|-----------------|-----------------:|----------:|---------:|----------:|-------------------------:|-----------:|
| Onyx:getAllKeys |           1.2min |   2.16sec |  0.159ms | 782.230ms |                 12.55sec |         90 |
| Onyx:merge      |          4.73sec |   2.00sec | 74.412ms | 591.642ms |                 10.24sec |          8 |
| Onyx:set        |          3.90sec | 846.760ms | 43.663ms | 433.056ms |                  7.47sec |          9 |
| Onyx:get        |          8.87sec |   2.00sec |  0.063ms |  61.998ms |                 10.24sec |        143 |


|                           Onyx:set                            |
|---------------------------------------------------------------|
| start time | end time  | duration  |           args           |
|-----------:|----------:|----------:|--------------------------|
|  291.042ms | 553.079ms | 262.037ms | session, [object Object] |
|  293.719ms | 553.316ms | 259.597ms | account, [object Object] |
|  294.541ms | 553.651ms | 259.109ms | network, [object Object] |
|  365.378ms | 554.246ms | 188.867ms | iou, [object Object]     |
|    1.08sec |   2.20sec |   1.12sec | network, [object Object] |
|    1.08sec |   2.20sec |   1.12sec | iou, [object Object]     |
|    1.17sec |   2.20sec |   1.03sec | currentURL, /            |

Debug mode

It can be useful to log why Onyx is calling setState() on a particular React component so that we can understand which key changed, what changed about the value, and the connected component that ultimately rendered as a result. When used correctly this can help isolate problem areas and unnecessary renders in the code. To enable this feature, pass debugSetState: true to the config and grep JS console logs for [Onyx-Debug].

Development

react-native bundles source using the metro bundler. metro does not follow symlinks, so we can't use npm link to link a local version of Onyx during development

To quickly test small changes you can directly go to node_modules/react-native-onyx in the parent project and:

• tweak original source if you're testing over a react-native project
• tweak dist/web.development.js for non react-native-projects

To continuously work on Onyx we have to set up a task that copies content to parent project's node_modules/react-native-onyx:

1. Work on Onyx feature or a fix
2. Save files
3. Optional: run npm run build (if you're working or want to test on a non react-native project)
   • npm link would actually work outside of react-native and it can be used to link Onyx locally for a web only project
4. Copy Onyx to consumer project's node_modules/react-native-onyx