[PERF] optimise notifications when has-many array is changed

addon/-private/system/diff-array.js

@@ -0,0 +1,60 @@
+/**
+  @namespace
+  @method diff-array
+  @for DS
+  @param {Array} oldArray the old array
+  @param {Array} newArray the new array
+  @return {hash} {
+      firstChangeIndex: <integer>,  // null if no change
+      addedCount: <integer>,        // 0 if no change
+      removedCount: <integer>       // 0 if no change
+    }
+*/
+const diffArray = function (oldArray, newArray) {
+  const oldLength = oldArray.length;
+  const newLength = newArray.length;
+
+  const shortestLength = Math.min(oldLength, newLength);
+  let firstChangeIndex = null; // null signifies no changes
+
+  // find the first change
+  for (let i=0; i<shortestLength; i++) {
+    // compare each item in the array
+    if (oldArray[i] !== newArray[i]) {
+      firstChangeIndex = i;
+      break;
+    }
+  }
+
+  if (firstChangeIndex === null && newLength !== oldLength) {
+    // no change found in the overlapping block
+    // and array lengths differ,
+    // so change starts at end of overlap
+    firstChangeIndex = shortestLength;
+  }
+
+  let addedCount = 0;
+  let removedCount = 0;
+  if (firstChangeIndex !== null) {
+    // we found a change, find the end of the change
+    let unchangedEndBlockLength = shortestLength - firstChangeIndex;
+    // walk back from the end of both arrays until we find a change
+    for (let i=1; i<=shortestLength; i++) {
+      // compare each item in the array
+      if (oldArray[oldLength-i] !== newArray[newLength-i]) {
+        unchangedEndBlockLength = i-1;
+        break;
+      }
+    }
+    addedCount = newLength - unchangedEndBlockLength - firstChangeIndex;
+    removedCount = oldLength - unchangedEndBlockLength - firstChangeIndex;
+  }
+
+  return {
+    firstChangeIndex,
+    addedCount,
+    removedCount
+  };
+}
+
+export default diffArray;

addon/-private/system/many-array.js

@@ -3,8 +3,9 @@
 */
 import Ember from 'ember';
 import { assert } from "ember-data/-private/debug";
-import { PromiseArray } from "ember-data/-private/system/promise-proxies";
-import { _objectIsAlive } from "ember-data/-private/system/store/common";
+import { PromiseArray } from "./promise-proxies";
+import { _objectIsAlive } from "./store/common";
+import diffArray from './diff-array';
 
 const { get, set } = Ember;
 
@@ -146,26 +147,31 @@ export default Ember.Object.extend(Ember.MutableArray, Ember.Evented, {
 
     //a hack for not removing new records
     //TODO remove once we have proper diffing
-    let newRecords = this.currentState.filter(
+    const newRecords = this.currentState.filter(
       // only add new records which are not yet in the canonical state of this
       // relationship (a new record can be in the canonical state if it has
       // been 'acknowleged' to be in the relationship via a store.push)
       (internalModel) => internalModel.isNew() && toSet.indexOf(internalModel) === -1
     );
     toSet = toSet.concat(newRecords);
-    let oldLength = this.length;
-    this.arrayContentWillChange(0, this.length, toSet.length);
-    // It’s possible the parent side of the relationship may have been unloaded by this point
-    if (_objectIsAlive(this)) {
-      this.set('length', toSet.length);
-    }
-    this.currentState = toSet;
-    this.arrayContentDidChange(0, oldLength, this.length);
 
-    if (isInitialized) {
-      //TODO Figure out to notify only on additions and maybe only if unloaded
+    // diff to find changes
+    const diff = diffArray(this.currentState, toSet);
+
+    if (diff.firstChangeIndex !== null) { // it's null if no change found
+      // we found a change
+      this.arrayContentWillChange(diff.firstChangeIndex, diff.removedCount, diff.addedCount);
+      // It’s possible the parent side of the relationship may have been unloaded by this point
+      if (_objectIsAlive(this)) {
+        this.set('length', toSet.length);
+      }
+      this.currentState = toSet;
+      this.arrayContentDidChange(diff.firstChangeIndex, diff.removedCount, diff.addedCount);
       this.relationship.notifyHasManyChanged();
     }
+    if (isInitialized) {
+      this.record.updateRecordArrays();
+    }
   },
 
   internalReplace(idx, amt, objects) {
@@ -290,12 +296,11 @@ export default Ember.Object.extend(Ember.MutableArray, Ember.Evented, {
     @return {DS.Model} record
   */
   createRecord(hash) {
-    let store = get(this, 'store');
-    let type = get(this, 'type');
-    let record;
+    const store = get(this, 'store');
+    const type = get(this, 'type');
 
     assert(`You cannot add '${type.modelName}' records to this polymorphic relationship.`, !get(this, 'isPolymorphic'));
-    record = store.createRecord(type.modelName, hash);
+    const record = store.createRecord(type.modelName, hash);
     this.pushObject(record);
 
     return record;