FIX: Don't remove the `id` from the input to `createRecord`

app/assets/javascripts/discourse/models/store.js.es6

@@ -268,7 +268,9 @@ export default Ember.Object.extend({
 
   _hydrate(type, obj, root) {
     if (!obj) { throw "Can't hydrate " + type + " of `null`"; }
-    if (!obj.id) { throw "Can't hydrate " + type + " without an `id`"; }
+
+    const id = obj.id;
+    if (!id) { throw "Can't hydrate " + type + " without an `id`"; }
 
     root = root || obj;
 
@@ -278,13 +280,14 @@ export default Ember.Object.extend({
       this._hydrateEmbedded(type, obj, root);
     }
 
-    const existing = fromMap(type, obj.id);
+    const existing = fromMap(type, id);
     if (existing === obj) { return existing; }
 
     if (existing) {
       delete obj.id;
       const klass = this.container.lookupFactory('model:' + type) || RestModel;
       existing.setProperties(klass.munge(obj));
+      obj.id = id;
       return existing;
     }
 

test/javascripts/models/store-test.js.es6

@@ -19,6 +19,18 @@ test('createRecord without an `id`', function() {
   ok(!widget.get('id'), 'there is no id');
 });
 
+test("createRecord doesn't modify the input `id` field", () => {
+  const store = createStore();
+  const widget = store.createRecord('widget', {id: 1, name: 'hello'});
+
+  const obj = { id: 1, name: 'something' };
+
+  const other = store.createRecord('widget', obj);
+  equal(widget, other, 'returns the same record');
+  equal(widget.name, 'something', 'it updates the properties');
+  equal(obj.id, 1, 'it does not remove the id from the input');
+});
+
 test('createRecord without attributes', function() {
   const store = createStore();
   const widget = store.createRecord('widget');