Add a non-model field on a ModelSerializer in DRF 3

Question

How do add a non-model field on a ModelSerializer in DRF 3? i.e. add a field that does not exist on my actual model?

class TestSerializer(serializers.ModelSerializer):     url = serializers.HyperlinkedIdentityField(view_name='vote_detail')     non_field = serializers.CharField()  # no corresponding model property.       class Meta:         model = vote_model         fields = ("url", "non_field")      def create(self, validated_data):       print(direction=validated_data['non_field']) 

But DRF 3 gives me the error:

Got AttributeError when attempting to get a value for field `non_field` on serializer `TestSerializer`. The serializer field might be named incorrectly and not match any attribute or key on the `Test` instance. Original exception text was: 'Test' object has no attribute 'non_field'. 

I have searched stack DRF - ModelSerializer with a non-model write_only field and found a few solutions but these refer to DRF 2 where I'm using DRF 3. Is there a solution for this on this version?

Answer 1

class MySerializer(serializers.ModelSerializer):     write_only_char_field = serializers.CharField(write_only=True)     write_only_list_char_field = serializers.ListField(child=serializers.CharField(max_length=100, default=''), write_only=True)     empty_method_field = serializers.SerializerMethodField()     read_only_custom_model_field = serializers.CharField(source='custom_property', read_only=True)      def create(self, validated_data):         validated_data.pop('write_only_char_field', None)         validated_data.pop('write_only_list_char_field', None)         return super().create(validated_data) 

The serializers.CharField(write_only=True) and serializers.ListField(...) is a good solution to provide extra data to your .create() and .update() methods, as either a single string or a list of strings (you can mix ListField with other serializer field types).
With this method, you can also define def validate_write_only_char_field to implement some quick and simple validation.

serializers.SerializerMethodField() allows you to add some custom read-only field to your serializer output from a method defined on the serializer.

The read_only_custom_model_field would use a method on your model to read some data, not strictly a model field, but a custom method. I.e.

class MyModel(models.Model):     my_field = models.CharField(max_length=100)      @property     def custom_property(self):         return "Perform calculations, combine with related models, etc. etc."