django rest framework serialize a dictionary without create a model

Question

My data is like this, I want to serialize them without creating model for them.

[
  {'form': 1, 'count': 1},
  {'form': 2, 'count': 3}
]

serilize to

[
  {'form': 'my form name 1', 'count': 1},
  {'form': 'my form name 2', 'count': 3}
]

I want to serialize it with serializer, get form name form model by pk.

class EavForm(models.Model):
    name = models.CharField(max_length=300)
    order = models.IntegerField(default=1)


# serializer
class CustomSerializer(serializers.Serializer):
    form = serializers.PrimaryKeyRelatedField(queryset=EavForm.objects.all())
    count = serializers.IntegerField()

Some error like 'int' object has no attribute 'pk'

test in python control

d = [{'form': 1, 'count': 1}, {'form': 2, 'count': 1}]
s = CustomSerializer(d, many=True)
print(s.data)

# error
Traceback (most recent call last):
  File "backend/src/db_tools/del1.py", line 25, in <module>
    print(s.data)
  File "backend/lib/python3.7/site-packages/rest_framework/serializers.py", line 768, in data
    ret = super(ListSerializer, self).data
  File "backend/lib/python3.7/site-packages/rest_framework/serializers.py", line 262, in data
    self._data = self.to_representation(self.instance)
  File "backend/lib/python3.7/site-packages/rest_framework/serializers.py", line 686, in to_representation
    self.child.to_representation(item) for item in iterable
  File "backend/lib/python3.7/site-packages/rest_framework/serializers.py", line 686, in <listcomp>
    self.child.to_representation(item) for item in iterable
  File "backend/lib/python3.7/site-packages/rest_framework/serializers.py", line 530, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "backend/lib/python3.7/site-packages/rest_framework/relations.py", line 272, in to_representation
    return value.pk
AttributeError: 'int' object has no attribute 'pk'

Solution

What you want,can be achived by doing following changes.

class EavForm(models.Model):
    name = models.CharField(max_length=300)
    order = models.IntegerField(default=1)


# serializer
class EvaFormPKRelatedField(PrimaryKeyRelatedField):
    def get_queryset(self):
        return EavForm.objects.all()

    def to_representation(self, value):
        return value.name


class CustomSerializer(serializers.Serializer):
    form = EvaFormPKRelatedField()
    count = serializers.IntegerField()

# Assume EvaForm exist of id 1 and 2
data = [{'form': 1, 'count': 1}, {'form': 2, 'count': 1}]
s = CustomSerializer(data=data, many=True)
print(s.data) 
""" Output
[
  {'form': 'my form name 1', 'count': 1},
  {'form': 'my form name 2', 'count': 3}
]
"""

print(s.validated_data)
""" Output
[
  {'form': <EvaForm: Evaform object (1)>, 'count': 1},
  {'form': <EvaForm: Evaform object (2)>, 'count': 3}
]
"""

Please note that, there is changes in output of .data and .validated_data .

1. .data will give you value of PrimaryKeyRelatedField by calling .to_representation() method.

2. .validated_data will give you value of PrimaryKeyRelatedField by calling .to_internal_value() method. Because, validated data got it's value for each field by calling it's all validations, and internally before running validations each field value will be updated by calling it's to_internal_value() method and that value is used for validation process.