Using nested serializers with explicit ForeignKey binding replaced with raw IntegerField

Question

I'm trying to get rid of explicit binding between my models. Thus instead of using ForeignKey, I'll use IntegerField to just store the primary key of target model as a field. Thus I'll handle the relationship manually at code level. This is because, I'll have to move my some schemas to different database instances. So they can't have linkage.

Now, I'm facing issue with my nested serializer. I'm trying to create an instance of the below model:

 17 class Customer(models.Model):
 18     id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
 19     phone_no = models.CharField(max_length=15, unique=True)

And this is my CustomerAddress model, which references the Customer model:

 47 class CustomerAddress(models.Model):
 48     # customer = models.ForeignKey(Customer, related_name='cust_addresses')
 49     customer_id = models.UUIDField(default=uuid.uuid4)
 50     address = models.CharField(max_length=1000)

Below is my serializers:

  7 class CustomerAddressSerializer(serializers.ModelSerializer):
  8
  9     class Meta:
 10         model = CustomerAddress
 11         depth = 1

 31 class CustomerSerializer(serializers.ModelSerializer):
 32     cust_addresses = CustomerAddressSerializer(many=True)
 33
 34     class Meta:
 35         model = Customer
 36         depth = 1
 37         fields = ('id', 'phone_no', 'cust_addresses',)
 38
 39     def create(self, validated_data):
 40         cust = Customer.objects.create(id=uuid.uuid4())
 41
 42         for addr in validated_data['cust_addresses']:
 43             address = addr['address']
 44             cust_addr = CustomerAddress.objects.create(address=address, customer_id=cust.id)
 45
 46         return cust

My views:

 12 class CustomerView(generics.RetrieveAPIView, generics.CreateAPIView):
 13     serializer_class = CustomerSerializer
 14
 22     def get_object(self):
 23         session = self.request.session
 24         if session.has_key('uuid'):
 25             id = session['uuid']
 26             cust = Customer.objects.get(pk=uuid.UUID(id))
 27             return cust
 28         return None

When I try to fire the post request to above view from my test:

 71     def test_create_customer_address(self):
 72         cust_url = reverse('user_v1:customer')
 73         # Now we create a customer, and use it's UID in the "customer" data of /cust-address/
 74         cust_data = {"first_name": "Rohit", "last_name": "Jain", "phone_no": "xxxxxx", "email_id": "[email protected]", "cust_addresses": [{"city_id": 1, "address": "addr", "pin_code": "123124", "address_tag": "XYZ"}]}
 75         cust_response = self.client.post(cust_url, cust_data, format='json')
 76         print 'Post Customer'
 77         print cust_response
 78         self.assertEqual(cust_response.data['id'], str(cust_id))

My test is failing with the following error trace:

======================================================================
ERROR: test_create_customer_address (app.tests.CustomerViewTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ubuntu/src/django-proj/app/tests.py", line 75, in test_create_customer_address
    cust_response = self.client.post(cust_url, cust_data, format='json')
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/test.py", line 168, in post
    path, data=data, format=format, content_type=content_type, **extra)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/test.py", line 90, in post
    return self.generic('POST', path, data, content_type, **extra)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/compat.py", line 231, in generic
    return self.request(**r)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/test.py", line 157, in request
    return super(APIClient, self).request(**kwargs)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/test.py", line 109, in request
    request = super(APIRequestFactory, self).request(**kwargs)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/django/test/client.py", line 466, in request
    six.reraise(*exc_info)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 132, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
    return view_func(*args, **kwargs)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/django/views/generic/base.py", line 71, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/views.py", line 456, in dispatch
    response = self.handle_exception(exc)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/views.py", line 453, in dispatch
    response = handler(request, *args, **kwargs)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/generics.py", line 190, in post
    return self.create(request, *args, **kwargs)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/mixins.py", line 21, in create
    headers = self.get_success_headers(serializer.data)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/serializers.py", line 470, in data
    ret = super(Serializer, self).data
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/serializers.py", line 217, in data
    self._data = self.to_representation(self.instance)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/serializers.py", line 430, in to_representation
    attribute = field.get_attribute(instance)
  File "/home/ubuntu/Envs/rj-venv/local/lib/python2.7/site-packages/rest_framework/fields.py", line 317, in get_attribute
    raise type(exc)(msg)
AttributeError: Got AttributeError when attempting to get a value for field `cust_addresses` on serializer `CustomerSerializer`.
The serializer field might be named incorrectly and not match any attribute or key on the `Customer` instance.
Original exception text was: 'Customer' object has no attribute 'cust_addresses'.

----------------------------------------------------------------------

All this was working fine when I had my CustomerAddress have ForeignKey binding to Customer. I'm not getting any clue on how to fix this thing. I tried to look through the source code to see whether some customization needs to be done. But I'm at loss. I feel like I've to somehow tweak with my serializer, by may be overriding to_representation method, but I'm not sure.

BTW, error only comes while creating the model instance. For GET request, I get the proper json, with nested serializer.

Have anyone else tried to do something like this and succeeded? What should be done to make this work? And yes, I've to remove the explicit foreign key binding.

Answer 1

I would take REST framework out of the equation, and initially just look at how you want to manage this relationship at a model and manager/queryset level.

I'd start with what you have in your own answer, but perhaps make cust_addresses be a cached property, so you can prevent multiple lookups.

class Customer(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    phone_no = models.CharField(max_length=15, unique=True)

    # Only make the relationship query once.
    @cached_property
    def cust_addresses(self):
        return CustomerAddress.objects.filter(customer_id=self.id)

class CustomerAddress(models.Model):
    customer_id = models.UUIDField(default=uuid.uuid4)
    address = models.CharField(max_length=1000)

You can then consider adding pre-caching behavior in a customer manager/queryset class. For example, you could pre-cache the relationship when creating both a customer and their set of addresses:

class CustomerManager(models.Manager):
    def create(phone_no, cust_addresses):
        """
        Customers and addresses are always created together.

        Usage:

        CustomerManager.objects.create(
            phone_no='123',
            cust_addresses=[{'address': 'abc'}, {'address': 'def'}]
        )
        """
        customer = super(CustomerManager, self).create(phone_no=phone_no)
        addresses = [
            CustomerAddress.objects.create(
                customer_id=instance.id
                address=item['address']
            )
            for item in cust_addresses
        ]

        # When creating both Customer and Address instances,
        # we can pre-cache the relationship.
        customer.__dict__['cust_addresses'] = addresses

        return customer

Make sure to add objects = CustomerManager() to the Customer model class.

Then you just have the integration with REST framework serializers to deal with.

Note that I've dropped using ModelSerializer in favor of a plain Serializer class. For everything other than quick prototyping I'd tend to prefer this - what you lose in duplication you gain in simplicity and clarity.

class CustomerAddressSerializer(serializers.Serializer):
    address = serializers.CharField(max_length=1000)

class CustomerSerializer(serializers.Serializer):
    id = serializers.UUIDField(read_only=True)
    phone_no = serializers.CharField(max_length=15, validators=[UniqueValidator(queryset=Customer.objects.all())])
    cust_addresses = CustomerAddressSerializer(many=True)

    def create(self, validated_data):
        return Customer.objects.create(**validated_data)