From 9d6b56628ed21aebf7fff94cb7c0def0469c5991 Mon Sep 17 00:00:00 2001
From: Eric Hwang <e@lever.co>
Date: Fri, 28 Jul 2017 13:16:58 -0700
Subject: [PATCH 1/4] Change Query.idMap to count ids, to be defensive against
 duplicate ids in query results (see
 https://github.com/share/sharedb-mongo/issues/55)

---
 lib/Model/Query.js  | 12 +++++++++---
 test/Model/query.js | 26 ++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/lib/Model/Query.js b/lib/Model/Query.js
index f7c8b4824..585fc2f36 100644
--- a/lib/Model/Query.js
+++ b/lib/Model/Query.js
@@ -158,7 +158,7 @@ function Query(model, collectionName, expression, options) {
   // because otherwise maybeUnload would be looping through the entire results
   // set of each query on the same collection for every doc checked
   //
-  // Map of id -> true
+  // Map of id -> count of ids
   this.idMap = {};
 }
 
@@ -293,7 +293,12 @@ Query.prototype._shareSubscribe = function(options, cb) {
 Query.prototype._removeMapIds = function(ids) {
   for (var i = ids.length; i--;) {
     var id = ids[i];
-    delete this.idMap[id];
+    if (this.idMap[id] > 0) {
+      this.idMap[id]--;
+    }
+    if (this.idMap[id] === 0) {
+      delete this.idMap[id];
+    }
   }
   // Technically this isn't quite right and we might not wait the full unload
   // delay if someone else calls maybeUnload for the same doc id. However,
@@ -312,7 +317,8 @@ Query.prototype._removeMapIds = function(ids) {
 Query.prototype._addMapIds = function(ids) {
   for (var i = ids.length; i--;) {
     var id = ids[i];
-    this.idMap[id] = true;
+    this.idMap[id] = this.idMap[id] || 0;
+    this.idMap[id]++;
   }
 };
 Query.prototype._diffMapIds = function(ids) {
diff --git a/test/Model/query.js b/test/Model/query.js
index e8d69c03c..29cdc54c0 100644
--- a/test/Model/query.js
+++ b/test/Model/query.js
@@ -1,4 +1,5 @@
 var expect = require('../util').expect;
+var racer = require('../../lib');
 var Model = require('../../lib/Model');
 
 describe('query', function() {
@@ -14,4 +15,29 @@ describe('query', function() {
       expect(query.expression).eql([{x: null}, {x: {y: null, z: 0}}]);
     });
   });
+
+  describe('idMap', function() {
+    beforeEach('create in-memory backend and model', function() {
+      this.backend = racer.createBackend();
+      this.model = this.backend.createModel();
+    });
+    it('handles insert and remove of a duplicate id', function() {
+      var query = this.model.query('myCollection', {key: 'myVal'});
+      query.subscribe();
+      query.shareQuery.emit('insert', [
+        {id: 'a'},
+        {id: 'b'},
+        {id: 'c'},
+      ], 0);
+      // Add and immediately remove a duplicate id.
+      query.shareQuery.emit('insert', [
+        {id: 'a'},
+      ], 3);
+      query.shareQuery.emit('remove', [
+        {id: 'a'},
+      ], 3);
+      // 'a' is still present once in the results, should still be in the map.
+      expect(query.idMap).to.only.have.keys(['a', 'b', 'c']);
+    });
+  });
 });

From e4cc334e406caa2612e232f632a39a964815347f Mon Sep 17 00:00:00 2001
From: Eric Hwang <e@lever.co>
Date: Fri, 28 Jul 2017 16:13:23 -0700
Subject: [PATCH 2/4] Switch query.idMap check to use "> 0"

---
 lib/Model/subscriptions.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/Model/subscriptions.js b/lib/Model/subscriptions.js
index b7a94346c..e9d9147d7 100644
--- a/lib/Model/subscriptions.js
+++ b/lib/Model/subscriptions.js
@@ -191,7 +191,7 @@ Model.prototype._hasDocReferences = function(collectionName, id) {
     for (var hash in queries) {
       var query = queries[hash];
       if (!query.subscribeCount && !query.fetchCount) continue;
-      if (query.idMap[id]) return true;
+      if (query.idMap[id] > 0) return true;
     }
   }
 

From 34d63dc10714bcdc77991c73c11e1e4aba50d635 Mon Sep 17 00:00:00 2001
From: Eric Hwang <e@lever.co>
Date: Fri, 28 Jul 2017 16:14:27 -0700
Subject: [PATCH 3/4] Query#_addMapIds: Consolidate idMap update to one line

---
 lib/Model/Query.js | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/lib/Model/Query.js b/lib/Model/Query.js
index 585fc2f36..f47039c7b 100644
--- a/lib/Model/Query.js
+++ b/lib/Model/Query.js
@@ -317,8 +317,7 @@ Query.prototype._removeMapIds = function(ids) {
 Query.prototype._addMapIds = function(ids) {
   for (var i = ids.length; i--;) {
     var id = ids[i];
-    this.idMap[id] = this.idMap[id] || 0;
-    this.idMap[id]++;
+    this.idMap[id] = (this.idMap[id] || 0) + 1;
   }
 };
 Query.prototype._diffMapIds = function(ids) {

From 51673d7063d9d34516fe49dcfed3b263a9aa79e5 Mon Sep 17 00:00:00 2001
From: Eric Hwang <e@lever.co>
Date: Fri, 28 Jul 2017 16:20:26 -0700
Subject: [PATCH 4/4] Query#_removeMapIds: Refactoring to remove a conditional
 check

---
 lib/Model/Query.js | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/Model/Query.js b/lib/Model/Query.js
index f47039c7b..679f4b280 100644
--- a/lib/Model/Query.js
+++ b/lib/Model/Query.js
@@ -293,10 +293,9 @@ Query.prototype._shareSubscribe = function(options, cb) {
 Query.prototype._removeMapIds = function(ids) {
   for (var i = ids.length; i--;) {
     var id = ids[i];
-    if (this.idMap[id] > 0) {
+    if (this.idMap[id] > 1) {
       this.idMap[id]--;
-    }
-    if (this.idMap[id] === 0) {
+    } else {
       delete this.idMap[id];
     }
   }