[BUGFIX release] Guard against isDestroyed in ManyArray.flushCanonical

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

@@ -4,6 +4,7 @@
 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";
 
 var get = Ember.get;
 var set = Ember.set;
@@ -84,7 +85,10 @@ export default Ember.Object.extend(Ember.MutableArray, Ember.Evented, {
     toSet = toSet.concat(newRecords);
     var oldLength = this.length;
     this.arrayContentWillChange(0, this.length, toSet.length);
-    this.set('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);
     //TODO Figure out to notify only on additions and maybe only if unloaded

tests/integration/relationships/has-many-test.js

@@ -2700,3 +2700,65 @@ test("PromiseArray proxies createRecord to its ManyArray before the hasMany is l
     });
   });
 });
+
+test("unloading and reloading a record with hasMany relationship - #3084", function(assert) {
+  var user;
+  var message;
+
+  run(function() {
+    env.store.push({
+      data: [{
+        type: 'user',
+        id: 'user-1',
+        attributes: {
+          name: 'Adolfo Builes'
+        },
+        relationships: {
+          messages: {
+            data: [
+              { type: 'message', id: 'message-1' }
+            ]
+          }
+        }
+      }, {
+        type: 'message',
+        id: 'message-1'
+      }]
+    });
+
+    user = env.store.peekRecord('user', 'user-1');
+    message = env.store.peekRecord('message', 'message-1');
+
+    assert.equal(get(user, 'messages.firstObject.id'), 'message-1');
+    assert.equal(get(message, 'user.id'), 'user-1');
+  });
+
+  run(function() {
+    env.store.unloadRecord(user);
+  });
+
+  run(function() {
+    // The record is resurrected for some reason.
+    env.store.push({
+      data: [{
+        type: 'user',
+        id: 'user-1',
+        attributes: {
+          name: 'Adolfo Builes'
+        },
+        relationships: {
+          messages: {
+            data: [
+              { type: 'message', id: 'message-1' }
+            ]
+          }
+        }
+      }]
+    });
+
+    user = env.store.peekRecord('user', 'user-1');
+
+    assert.equal(get(user, 'messages.firstObject.id'), 'message-1');
+    assert.equal(get(message, 'user.id'), 'user-1');
+  });
+});