title: Django Rest-Framework nested serializer for POST
body: <p>I'm trying to write a nested serializer for User and Profile models and I'm following this example:</p>
  
  <pre><code>class UserSerializer(serializers.ModelSerializer):
      profile = ProfileSerializer()
  
      class Meta:
          model = User
          fields = ('username', 'email', 'profile')
  
      def create(self, validated_data):
          profile_data = validated_data.pop('profile')
          user = User.objects.create(**validated_data)
          Profile.objects.create(user=user, **profile_data)
          return user
  </code></pre>
  
  <p>But Im getting this error:</p>
  
  <pre><code>{
      "profile": {
          "user": [
              "This field is required."
          ]
      }
  }
  </code></pre>
  
  <p>I even tried to add it to validation exceptions, like this: </p>
  
  <pre><code>def get_validation_exclusions(self):
      exclusions = super(ProfileSerializer,
                         self).get_validation_exclusions()
      return exclusions + ['user']
  </code></pre>
  
  <p>I think I solved it by adding this:     </p>
  
  <pre><code>user = serializers.ModelField(model_field=Profile()._meta.get_field(
          'user'), required=False) 
  </code></pre>
  
  <p>But I'm not sure yet.</p>