Update Binding to support models with UUIDField as primary key (#528)

* Add custom TestUUIDModel for auto tests

* Update Binding to support models with UUIDField as primary key

Add and fix test_trigger_outbound_create_non_auto_pk.
Before updating pre_save_receiver, this new test failed with this error:

======================================================================
FAIL: test_trigger_outbound_create_non_auto_pk
(channels.tests.test_binding.TestsBinding)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\User\git\contribs\python\channels\channels\tests\test_binding.py", line 85, in test_trigger_outbound_create_non_auto_pk
    self.assertEqual(received['payload']['action'], 'create')
AssertionError: u'update' != u'create'

channels/binding/base.py

@@ -120,7 +120,8 @@ class Binding(object):
 
     @classmethod
     def pre_save_receiver(cls, instance, **kwargs):
-        cls.pre_change_receiver(instance, CREATE if instance.pk is None else UPDATE)
+        creating = instance._state.adding
+        cls.pre_change_receiver(instance, CREATE if creating else UPDATE)
 
     @classmethod
     def post_save_receiver(cls, instance, created, **kwargs):

channels/tests/models.py

@@ -0,0 +1,12 @@
+from uuid import uuid4
+
+from django.db import models
+
+
+class TestUUIDModel(models.Model):
+    """
+    Simple model with UUIDField as primary key for tests.
+    """
+
+    id = models.UUIDField(primary_key=True, default=uuid4)
+    name = models.CharField(max_length=255)

channels/tests/settings.py

@@ -6,7 +6,8 @@ INSTALLED_APPS = (
     'django.contrib.sessions',
     'django.contrib.admin',
     'channels',
-    'channels.delay'
+    'channels.delay',
+    'channels.tests'
 )
 
 DATABASES = {

channels/tests/test_binding.py

@@ -6,7 +6,7 @@ from channels import route
 from channels.binding.base import CREATE, DELETE, UPDATE
 from channels.binding.websockets import WebsocketBinding
 from channels.generic.websockets import WebsocketDemultiplexer
-from channels.tests import ChannelTestCase, HttpClient, apply_routes
+from channels.tests import ChannelTestCase, HttpClient, apply_routes, models
 
 User = get_user_model()
 
@@ -55,6 +55,42 @@ class TestsBinding(ChannelTestCase):
         received = client.receive()
         self.assertIsNone(received)
 
+    def test_trigger_outbound_create_non_auto_pk(self):
+
+        class TestBinding(WebsocketBinding):
+            model = models.TestUUIDModel
+            stream = 'test'
+            fields = ['name']
+
+            @classmethod
+            def group_names(cls, instance):
+                return ["testuuidmodels"]
+
+            def has_permission(self, user, action, pk):
+                return True
+
+        client = HttpClient()
+        client.join_group('testuuidmodels')
+
+        instance = models.TestUUIDModel.objects.create(name='testname')
+
+        received = client.receive()
+        self.assertTrue('payload' in received)
+        self.assertTrue('action' in received['payload'])
+        self.assertTrue('data' in received['payload'])
+        self.assertTrue('name' in received['payload']['data'])
+        self.assertTrue('model' in received['payload'])
+        self.assertTrue('pk' in received['payload'])
+
+        self.assertEqual(received['payload']['action'], 'create')
+        self.assertEqual(received['payload']['model'], 'tests.testuuidmodel')
+        self.assertEqual(received['payload']['pk'], str(instance.pk))
+
+        self.assertEqual(received['payload']['data']['name'], 'testname')
+
+        received = client.receive()
+        self.assertIsNone(received)
+
     def test_trigger_outbound_create_exclude(self):
         class TestBinding(WebsocketBinding):
             model = User