Implement an equivalent for Parse.Query.count()

src/ParsePatches.js

@@ -61,6 +61,14 @@ var patches = {
     return this.equalTo('objectId', objectId).limit(1);
   },
 
+  /**
+   * The ParseReact equivalent to Parse.Query(...).count()
+   */
+  observeCount: function() {
+    this._observeCount = true;
+    return this;
+  },
+
   /**
    * Patches for Parse.User to watch for user signup / login / logout
    */
@@ -99,6 +107,9 @@ var ParsePatches = {
     if (!Parse.Query.prototype.observeOne) {
       Parse.Query.prototype.observeOne = patches.observeOne;
     }
+    if (!Parse.Query.prototype.observeCount) {
+      Parse.Query.prototype.observeCount = patches.observeCount;
+    }
     pointerMethods.forEach(function(method) {
       var old = Parse.Query.prototype[method];
       Parse.Query.prototype[method] = function(attr, value) {

src/QueryTools.js

@@ -156,6 +156,9 @@ function matchesQuery(
     if (className !== query.className) {
       return false;
     }
+    if (query._observeCount) {
+      return false;
+    }
     return matchesQuery(object, query._where);
   }
   for (var field in query) {

src/Subscription.js

@@ -91,6 +91,7 @@ class Subscription {
   pending: boolean;
   subscribers: { [key: string]: Subscriber };
   resultSet: Array<Id | IdWithOrderingInfo>;
+  resultCount: ?number;
   observationCount: number;
 
   constructor(query: ParseQuery) {
@@ -102,6 +103,7 @@ class Subscription {
     this.subscribers = {};
     // The Ids of the objects returned by this Subscription's query
     this.resultSet = [];
+    this.resultCount = null;
 
     this.observationCount = 0;
 
@@ -118,9 +120,13 @@ class Subscription {
     var oid = 'o' + this.observationCount++;
     this.subscribers[oid] = callbacks;
 
-    var resultSet = this.resultSet.map(extractId);
-    var data = resultSet.length ? ObjectStore.getDataForIds(resultSet) : [];
-    callbacks.onNext(this.originalQuery._observeOne ? data[0] : data);
+    if (this.originalQuery._observeCount) {
+      callbacks.onNext(this.resultCount);
+    } else {
+      var resultSet = this.resultSet.map(extractId);
+      var data = resultSet.length ? ObjectStore.getDataForIds(resultSet) : [];
+      callbacks.onNext(this.originalQuery._observeOne ? data[0] : data);
+    }
 
     return oid;
   }
@@ -146,17 +152,27 @@ class Subscription {
    */
   issueQuery() {
     this.pending = true;
+    var errorHandler = (err) => {
+      this.pending = false;
+      this.pushError(err);
+    };
+
+    if (this.originalQuery._observeCount) {
+      this.originalQuery.count().then((result) => {
+        this.pending = false;
+        this.resultCount = result;
+        this._forEachSubscriber((subscriber) => subscriber.onNext(result));
+      }, errorHandler);
+      return;
+    }
     this.originalQuery.find().then((results) => {
       this.pending = false;
       this.resultSet = ObjectStore.storeQueryResults(
         results,
         this.originalQuery
       );
       this.pushData();
-    }, (err) => {
-      this.pending = false;
-      this.pushError(err);
-    });
+    }, errorHandler);
   }
 
   /**