Django Rest Framework ModelSerializer custom serializer field to_internal_value doesn't save to object

Question

I have model and serializer, there is ArrayField(postgres) in that model.

Now I wanted to create a serializer field that will receive list [1,2] and save it to object, but for a list and detail in serializer to show a list of JSON objects.

Model:

class User(models.Model):
    email = models.EmailField('Email', unique=True, blank=False)
    full_name = models.CharField(
        'Full name', max_length=150, blank=True, null=True)
    roles = ArrayField(
        models.PositiveSmallIntegerField(),
        default=list,
        blank=True
    )

Serializer:

class ArraySerializerField(ListField):

    def __init__(self, queryset, serializer_class):
        super(ArraySerializerField, self).__init__()
        self.queryset = queryset
        self.serializer_class = serializer_class

    def to_representation(self, value):
        if value:
            qs = self.queryset.filter(pk__in=value)
            return self.serializer_class(qs, many=True).data

        return []

    def to_internal_value(self, value):
        super(ArraySerializerField, self).to_internal_value(value)
        print(value)  # [1, 2]
        return value


class UserSerializer(SerializerExtensionsMixin, serializers.ModelSerializer):
    roles = ArraySerializerField(queryset=Role.objects.all(), serializer_class=RoleSerializer)

    class Meta:
        model = User
        fields = ('id', 'email', 'full_name', 'roles')

    def create(self, validated_data):
        print(validated_data) 
        # {'email': 'test@test.com', 'full_name': 'Test', 'roles': []}
        user = super(UserSerializer, self).create(validated_data)

        return user

Now when I do list or detail request, everything is ok, I get a list of roles as JSON.

But when I try to POST data and send with this data:

{
  "email": "test@test.com",
  "full_name": "Test",
  "roles": [1, 2]
}

validated_data in create method shows roles always as [] and object is saved without roles, but print from to_internal_value shows [1, 2] .

What am I doing wrong? It should save sent data because to_internal_value works fine.

EDIT:

GET and LIST response gives me right format:

{
  "id": 1,
  "email": "test@test.com",
  "full_name": "Test",
  "roles": [
    {
      "id": 1,
      "name": "Role 1"
    },
    {
      "id": 2,
      "name": "Role 2"
    }
  ]
}

Answer 1

Have you tried this?

class UserSerializer(SerializerExtensionsMixin, serializers.ModelSerializer):
    

    class Meta:
        model = User
        fields = ('id', 'email', 'full_name', 'roles')

    def create(self, validated_data):
        # check validated_data here
        ...

Note

I'm not sure about the nature of SerializerExtensionsMixin class here. Also I'm not sure the intention behind the queryset and serializer_class arguments of your custom ListField

---

Django Shell Output

In [7]: from rest_framework import serializers                                                                                                                                                                     

In [8]: class UserSerializer(serializers.Serializer): 
   ...:     roles = serializers.ListField(child=serializers.IntegerField(), allow_empty=True, required=False) 
   ...:     email = serializers.EmailField() 
   ...:     full_name = serializers.CharField() 
   ...:                                                                                                                                                                                                            

In [9]: data = { 
   ...:   "email": "test@test.com", 
   ...:   "full_name": "Test", 
   ...:   "roles": [1, 2] 
   ...: }                                                                                                                                                                                                          

In [10]: u = UserSerializer(data=data)                                                                                                                                                                             

In [11]: u.is_valid()                                                                                                                                                                                              
Out[11]: True

In [12]: u.data                                                                                                                                                                                                    
Out[12]: {'roles': [1, 2], 'email': 'test@test.com', 'full_name': 'Test'}

In [13]: data["roles"] = []                                                                                                                                                                                        

In [14]: u = UserSerializer(data=data)                                                                                                                                                                             

In [15]: u.is_valid()                                                                                                                                                                                              
Out[15]: True

In [16]: u.data                                                                                                                                                                                                    
Out[16]: {'roles': [], 'email': 'test@test.com', 'full_name': 'Test'} 

In [17]: data["roles"] = ["foo","bar"]                                                                                                                                                                             

In [18]: u = UserSerializer(data=data)                                                                                                                                                                             

In [19]: u.is_valid()                                                                                                                                                                                           
Out[19]: False

In [20]: u.errors                                                                                                                                                                                                  
Out[20]: {'roles': {0: [ErrorDetail(string='A valid integer is required.', code='invalid')], 1: [ErrorDetail(string='A valid integer is required.', code='invalid')]}}

---

UPDATE-1

Create a RoleSerializer and use it in the UserSerializer

class UserSerializer(SerializerExtensionsMixin, serializers.ModelSerializer):
    roles = serializers.ListField(child=serializers.IntegerField(), allow_empty=True, required=False)

    class Meta:
        model = User
        fields = ('id', 'email', 'full_name', 'roles')

    def create(self, validated_data):
        # check validated_data here
        ...

    

---

UPDATE-2

Using a custom array field

class UserSerializer(SerializerExtensionsMixin, serializers.ModelSerializer):
    

    class Meta:
        model = User
        fields = ('id', 'email', 'full_name', 'roles')

    def create(self, validated_data):
        # check validated_data here
        ...

Answer 2

Try switching to PrimaryKeyRelatedField . Though you'll need to change your user model to use an actual relation. Which is generally a good idea because it'll help enforce data integrity with your project.

class User(models.Model):
    email = models.EmailField('Email', unique=True, blank=False)
    full_name = models.CharField(
        'Full name', max_length=150, blank=True, null=True)
    roles = models.ManyToManyField(Role, blank=True)

class UserSerializer(SerializerExtensionsMixin, serializers.ModelSerializer):
    roles = serializers.PrimaryKeyRelatedField(
        many=True,
        queryset=Role.objects.all(),
    )

    class Meta:
        model = User
        fields = ('id', 'email', 'full_name', 'roles')

    def create(self, validated_data):
        print(validated_data) 
        # {'email': 'test@test.com', 'full_name': 'Test', 'roles': []}
        user = super(UserSerializer, self).create(validated_data)

        return user