Clear m2m relationships instead of deleting related objects during PATCH (#788)

Fixes #784
Fixes #244 

Co-authored-by: Oliver Sauder <os@esite.ch>

Author: rohithpr

AUTHORS

@@ -17,6 +17,7 @@ Ola Tarkowska <ola@red-aries.com>
 Oliver Sauder <os@esite.ch>
 Raphael Cohen <raphael.cohen.utt@gmail.com>
 Roberto Barreda <roberto.barreda@gmail.com>
+Rohith PR <praroh2@gmail.com>
 santiavenda <santiavenda2@gmail.com>
 Tim Selman <timcbaoth@gmail.com>
 Yaniv Peer <yanivpeer@gmail.com>

CHANGELOG.md

@@ -17,6 +17,7 @@ any parts of the framework not mentioned in the documentation should generally b
 ### Fixed
 
 * Avoid `AttributeError` for PUT and PATCH methods when using `APIView`
+* Clear many-to-many relationships instead of deleting related objects during PATCH on `RelationshipView`
 
 ### Changed
 

example/tests/test_views.py

@@ -135,6 +135,26 @@ def test_patch_one_to_many_relationship(self):
         response = self.client.get(url)
         assert response.data == request_data['data']
 
+        # retry a second time should end up with same result
+        response = self.client.patch(url, data=request_data)
+        assert response.status_code == 200, response.content.decode()
+        assert response.data == request_data['data']
+
+        response = self.client.get(url)
+        assert response.data == request_data['data']
+
+    def test_patch_one_to_many_relaitonship_with_none(self):
+        url = '/blogs/{}/relationships/entry_set'.format(self.first_entry.id)
+        request_data = {
+            'data': None
+        }
+        response = self.client.patch(url, data=request_data)
+        assert response.status_code == 200, response.content.decode()
+        assert response.data == []
+
+        response = self.client.get(url)
+        assert response.data == []
+
     def test_patch_many_to_many_relationship(self):
         url = '/entries/{}/relationships/authors'.format(self.first_entry.id)
         request_data = {
@@ -152,6 +172,14 @@ def test_patch_many_to_many_relationship(self):
         response = self.client.get(url)
         assert response.data == request_data['data']
 
+        # retry a second time should end up with same result
+        response = self.client.patch(url, data=request_data)
+        assert response.status_code == 200, response.content.decode()
+        assert response.data == request_data['data']
+
+        response = self.client.get(url)
+        assert response.data == request_data['data']
+
     def test_post_to_one_relationship_should_fail(self):
         url = '/entries/{}/relationships/blog'.format(self.first_entry.id)
         request_data = {

rest_framework_json_api/views.py

@@ -286,6 +286,8 @@ def remove_relationships(self, instance_manager, field):
             for obj in instance_manager.all():
                 setattr(obj, field_object.name, None)
                 obj.save()
+        elif hasattr(instance_manager, 'clear'):
+            instance_manager.clear()
         else:
             instance_manager.all().delete()