Writable nested serializer error with UniqueTogetherValidator

[hiepthai]

Encountered this strange error, any idea what i'm missing?
Django Version: 1.7
Python Version: 2.7.3
DRF: 3.0.2

# Model
class Pin(BaseModel):
    user = models.ForeignKey(User)
    item = models.ForeignKey(Photo)
    board = models.ForeignKey(Board)

    class Meta:
        unique_together = ('item', 'board')

# Serializer
class PinSerializer(serializers.ModelSerializer):
    user = UserSerializer(read_only=True)
    board = BoardSerializer()

    class Meta:
        model = Pin
        fields = ('id', 'user', 'item', 'board')

    def create(self, validated_data):
        board_data = validated_data.pop('board')
        board_name = board_data.get('name', 'My favorites')
        user = validated_data.get('user', None)
        board, created = Board.objects.get_or_create(name=board_name, user=user)
        return Pin.objects.create(board=board, **validated_data)

Traceback:
File "/home/django/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response

1.                 response = wrapped_callback(request, _callback_args, *_callback_kwargs)
   

   File "/home/django/local/lib/python2.7/site-packages/django/views/decorators/csrf.py" in wrapped_view

2.     return view_func(_args, *_kwargs)
   

   File "/home/django/local/lib/python2.7/site-packages/rest_framework/viewsets.py" in view

3.         return self.dispatch(request, _args, *_kwargs)
   

   File "/home/django/local/lib/python2.7/site-packages/rest_framework/views.py" in dispatch

4.         response = self.handle_exception(exc)
   

   File "/home/django/local/lib/python2.7/site-packages/rest_framework/views.py" in dispatch

5.         response = handler(request, _args, *_kwargs)
   

   File "/home/django/local/lib/python2.7/site-packages/rest_framework/mixins.py" in create

6.     serializer.is_valid(raise_exception=True)
   

   File "/home/django/local/lib/python2.7/site-packages/rest_framework/serializers.py" in is_valid

7.             self._validated_data = self.run_validation(self.initial_data)
   

   File "/home/django/local/lib/python2.7/site-packages/rest_framework/serializers.py" in run_validation

8.         self.run_validators(value)
   

   File "/home/django/local/lib/python2.7/site-packages/rest_framework/fields.py" in run_validators

9.             validator(value)
   

   File "/home/django/local/lib/python2.7/site-packages/rest_framework/validators.py" in call

10.     queryset = self.filter_queryset(attrs, queryset)
    

    File "/home/django/local/lib/python2.7/site-packages/rest_framework/validators.py" in filter_queryset

11.     return queryset.filter(**filter_kwargs)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/manager.py" in manager_method

12.             return getattr(self.get_queryset(), name)(_args, *_kwargs)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/query.py" in filter

13.     return self._filter_or_exclude(False, _args, *_kwargs)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/query.py" in _filter_or_exclude

14.         clone.query.add_q(Q(_args, *_kwargs))
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/sql/query.py" in add_q

15.     clause, require_inner = self._add_q(where_part, self.used_aliases)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/sql/query.py" in _add_q

16.                 current_negated=current_negated, connector=connector)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/sql/query.py" in build_filter

17.                                                 lookups, value)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/fields/related.py" in get_lookup_constraint

18.                 lookup_class(Col(alias, target, source), val), AND)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/lookups.py" in init

19.     self.rhs = self.get_prep_lookup()
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/lookups.py" in get_prep_lookup

20.     return self.lhs.output_field.get_prep_lookup(self.lookup_name, self.rhs)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/fields/init.py" in get_prep_lookup

21.         return self.get_prep_value(value)
    

    File "/home/django/local/lib/python2.7/site-packages/django/db/models/fields/init.py" in get_prep_value

22.     return int(value)
    

Exception Type: TypeError at /api/v1/pin/
Exception Value: int() argument must be a string or a number, not 'OrderedDict'

[tomchristie]

The model serializer here is generating a UniqueTogetherValidator for item and board, although because board is a nested object it's passing the dictionary of data for it rather than a primary key.

We'll want to look into handling this more gracefully and documenting some of the constraints that unique together validators cannot automatically be applied too.

In the immediate case you'll probably want to turn of the default validators by instead specifying...

class Meta:
    validators = []

Then add the validation in explicitly.

def validate(self, attrs):
    # Ensure that a `Pin` with board_name=attrs['board']['name'] and item=attrs['item'] does not already exist.

You probably want to stop using ModelSerializer and just use a fully explicit serializer at this point too, since you're already overriding most of the fields, and the create method.

[tomchristie]

Also an off-topic point...

user = validated_data.get('user', None)

You've put read_only=True on the user field, so it will always be None.

[xordoquy]

We're missing a feedback on this. I'm going to close it.
Moreover, I'm going to assume #2975 fixes the unique together issue would there still be one.
Feel free to reopen if you have more about this.

[bjarnoldus]

I think this bug is still open. At least in 3.2.4 i got the same error:

self <UniqueTogetherValidator(queryset=Foo.objects.all(), fields=('foo', 'ip'))>
queryset Error in formatting: DataError: invalid input syntax for type inet: "OrderedDict([('address', '5.3.2.5')])" LINE 1: ...foo" WHERE ("foo"."ip_id" = 'OrderedDi...

attrs {'foo': <Foo: foo>, 'ip': OrderedDict([('address', '5.3.2.5')])}

[xordoquy]

the OP issue is to my opinion linked to opposite constraints (write unique together with a read only field).

[bjarnoldus]

I don't know if the 'read only' field changes the behavior. I've a unique constraint on two foreign keys, where the second one is an IP address. I needed to add the 'validators=[]" statement to Meta to turn off the validators. In some way the validator cannot handle complex unique_together constraints. For me it is solved using the proposed workaround, but maybe the unique_together in the library should be extended to handle these kind of fields.

[xordoquy]

This sounds like a different issue. Would help if you could come with a failing test case

[cderwin]

I'm still experiencing this issue (Django 1.9, DRF 3.3, Python 2.7). I don't have a test case at the moment, but I'll try to post one over the long weekend.