{Backport beta} [BUGFIX beta] Failing test for #5125 and attempted fix

addon/-private/system/store.js

@@ -1978,6 +1978,11 @@ Store = Service.extend({
       return;
     }
 
+    let existingInternalModel = this._existingInternalModelForId(modelName, id);
+
+    assert(`'${modelName}' was saved to the server, but the response returned the new id '${id}', which has already been used with another record.'`,
+      isNone(existingInternalModel) || existingInternalModel === internalModel);
+
     this._internalModelsFor(internalModel.modelName).set(id, internalModel);
 
     internalModel.setId(id);
@@ -2558,27 +2563,31 @@ Store = Service.extend({
 
     assert(`You can no longer pass a modelClass as the first argument to store._buildInternalModel. Pass modelName instead.`, typeof modelName === 'string');
 
-    let internalModels = this._internalModelsFor(modelName);
-    let existingInternalModel = internalModels.get(id);
-
-    if (existingInternalModel && existingInternalModel.hasScheduledDestroy()) {
-      // unloadRecord is async, if one attempts to unload + then sync create,
-      // we must ensure the unload is complete before starting the create
-      existingInternalModel.destroySync();
-      existingInternalModel = null;
-    }
+    let existingInternalModel = this._existingInternalModelForId(modelName, id);
 
     assert(`The id ${id} has already been used with another record for modelClass '${modelName}'.`, !existingInternalModel);
 
     // lookupFactory should really return an object that creates
     // instances with the injections applied
     let internalModel = new InternalModel(modelName, id, this, data);
 
-    internalModels.add(internalModel, id);
+    this._internalModelsFor(modelName).add(internalModel, id);
 
     return internalModel;
   },
 
+  _existingInternalModelForId(modelName, id) {
+    let internalModel = this._internalModelsFor(modelName).get(id);
+
+    if (internalModel && internalModel.hasScheduledDestroy()) {
+      // unloadRecord is async, if one attempts to unload + then sync create,
+      // we must ensure the unload is complete before starting the create
+      internalModel.destroySync();
+      internalModel = null;
+    }
+    return internalModel;
+  },
+
   buildInternalModel(modelName, id, data) {
     deprecate('buildInternalModel was documented as private and will be removed in the next version of Ember Data.', false, { id: 'ember-data.buildInternalModel', until: '2.17.0' });
     return this._buildInternalModel(modelName, id, data);

tests/integration/records/unload-test.js

@@ -647,3 +647,31 @@ test("after unloading a record, the record can be fetched again soon there after
 
   assert.equal(internalModel.currentState.stateName, 'root.loaded.saved', 'We are loaded after findRecord');
 });
+
+test('after unloading a record, the record can be saved again immediately', function (assert) {
+  assert.expect(0);
+
+  const store = env.store;
+  const data = {
+    data: {
+      type: 'person',
+      id: '1',
+      attributes: {
+        name: 'Adam Sunderland'
+      }
+    }
+  };
+
+  env.adapter.createRecord = () => Ember.RSVP.Promise.resolve(data);
+
+  run(() => {
+    // add an initial record with id '1' to the store
+    store.push(data);
+
+    // unload the initial record
+    store.peekRecord('person', '1').unloadRecord();
+
+    // create a new record that will again get id '1' from the backend
+    store.createRecord('person').save();
+  });
+});