Relationship deletion

[Reizoukodesu]

Allow the deletion of relationships using the relationships values of a request, eg:

{
  "data": {
     "id": 1,
     "type": "model",
     "attributes": {
       "name": "test-model",
       "number": 1
     },
     "relationships": {
       "other-model": {"data": null}
     }
  }
}

See JSON API specification

References #169

[jerel]

This looks good, thanks! Would you mind adding a test to this file to demonstrate the fix? https://github.com/django-json-api/django-rest-framework-json-api/blob/develop/example/tests/test_views.py#L140-L146 You can use the highlighted test as an example.

[Reizoukodesu]

Added a unit test for relationship deletion using the relationships attribute. I've used the blog field of an Entry instance. But as this field cannot be Null, the exception message is being tested and compared to "This field may not be null."

[jsenecal]

This does not test the added functionality unfortunately... Any idea on what to add to the example code to have a nullable to-one relationship?

[abdulhaq-e]

I think the model can be redefined inside the test function.

[Reizoukodesu]

After a closer look at the Model classes I've found a working use case, so I changed the deletion test to use the author relation field from the second comment.

[jerel]

Thank you!

[jsenecal]

Yes, thank you :) can we close #169?