Inherited serializers

[fredericcambon]

We recently upgraded to DRF 3.0 and noticed an important change of behaviour with the serializers.

For performance reasons, we implemented serializers in DRF 2.X that inherited each other to stay as DRY as possible. For one type of model we sometimes have up to 5/6 sub serializers

class TestSerializer(serializers.ModelSerializer):
    a = serializers.SerializerMethodField('get_a')

    class Meta:
        model = TestModel
        fields = ['a', 'b', 'c']

    def get_a(self, obj):
        return 0


class TestSubSerializer(TestSerializer):
    class Meta:
        model = TestModel
        fields = ['a']

This is useful because we don't have to rewrite get_a for each subserializer.

However this does not work in 3.0 because the __new__,__init__ methods of SerializerMetaclass retrieve the declared_fields of the current serializer class, not of its parents.
The following classes (with real code obviously) throw this error :

ImproperlyConfigured: Field name 'a' is not valid for model ModelBase.

It does so because a = serializers.serializers.SerializerMethodField('get_a') is declared in the parent class

Perhaps we are doing something wrong and not using the serializers properly ?

Thank you for your answer

[tomchristie]

Either related to, or duplicate of #2388 - haven't determined which yet.
In short tho - yes we should be supporting the inheritance case shown above so that's certainly something we'll prioritize getting fixed.

[tomchristie]

Copied your example as a test case, but does not reproduce...

from rest_framework import serializers
from django.db import models

class TestModel(models.Model):
    b = models.IntegerField()
    c = models.IntegerField()

class TestSerializer(serializers.ModelSerializer):
    a = serializers.SerializerMethodField('get_a')

    class Meta:
        model = TestModel
        fields = ['a', 'b', 'c']

    def get_a(self, obj):
        return 0

class TestSubSerializer(TestSerializer):
    class Meta:
        model = TestModel
        fields = ['a']

def test_sub():
    TestSubSerializer()

Closing this off, but still continuing with the valid #2388.

Can reopen this is a failing test case is supplied as a pull request, or the question is otherwise clarified.
Perhaps this was an earlier issue that is now resolved in 3.0.3

[fredericcambon]

#2388 is the same issue, the workaround provided solved my problem.

Thank you !

[aryabartar]

I came up with the exact same problem,
My DRF version is 3.9.4 but I can't inherit serializer fields in subclass and I have to redefine that field in each subclass.