Django REST Framework: Unique_together validation on Serializers

Question

Having issues with a serializer.is_valid() returning True if the serializer instance fails a unique_together constraint on the model side.

Is there a way for me to specify in the serializer to enforce a unique_together constraint?

Answer 1

The ModelSerializer class has this functionality build-in, at least in djangorestframework>=3.0.0, however if you are using a serializer which doesn't include all of the fields which are affected by your unique_togetherconstrain, then you'll get an IntegrityError when saving an instance which violates it. For example, using the following model:

class Foo(models.Model):     class Meta:         unique_together = ('foo_a', 'foo_b')      a = models.TextField(blank=True)     b = models.TextField(blank=True)     foo_a = models.IntegerField()     foo_b = models.IntegerField(default=2) 

and the following serializer and ViewSet:

class FooSerializer(serializers.ModelSerializer):     class Meta:         model = models.Foo         fields = ('a', 'b', 'foo_a')  class FooViewSet(viewsets.ModelViewSet):     queryset = models.Foo.objects.all()     serializer_class = FooSerializer   routes = routers.DefaultRouter() routes.register(r'foo', FooViewSet) 

if you try to save two instances with the same foo_a and foo_b set, you'll get an IntegrityError. However, if we modify the serializer like this:

class FooSerializer(serializers.ModelSerializer):     class Meta:         model = models.Foo         fields = ('a', 'b', 'foo_a', 'foo_b') 

you'll then get a proper HTTP 400 BAD REQUEST status code, and the corresponding JSON descriptive message in the response body:

HTTP 400 BAD REQUEST Content-Type: application/json Vary: Accept Allow: GET, POST, HEAD, OPTIONS  {     "non_field_errors": [         "The fields foo_a, foo_b must make a unique set."     ] } 

I hope this to result helpful for you, even when this is a somewhat old-posted question ;-)