context in nested serializers django rest framework

Question

If i have a nested serializer:

class ChildSerializer(ModelSerializer):     class Meta:         fields = ('c_name', )         model = Child   class ParentSerializer(ModelSerializer):      child = ChildSerializer(many=True, read_only=True)      class Meta:         model = Parent         fields = ('p_name', 'child') 

And i want to access the context in the nested serializer, how can i do that? As far as i can tell, context isn't passed to the Child.

I want to be able to implement a permission model per user on fields, for that i overridden the get_fields() method of the ModelSerializer:

def get_fields(self):     fields = super().get_fields()     ....     for f in fields:         if has_rights(self.context['request'].user, f, "read"):             ret_val[f] = fields[f]     ....     return ret_val 

Which works for regular serializers, but the context, and thus the request and user are not available when the nested child is passed to get_fields(). How do i access the context when the serializer is nested?

Answer 1

Ok i found a working solution. I replaced the ChildSerializer assignment in the Parent class with a SerializerMethodField which adds the context. This is then passed to the get_fields method in my CustomModelSerializer:

class ChildSerializer(CustomModelSerializer):     class Meta:         fields = ('c_name', )         model = Child   class ParentSerializer(CustomModelSerializer):      child = serializers.SerializerMethodField('get_child_serializer')      class Meta:         model = Parent         fields = ('p_name', 'child')      def get_child_serializer(self, obj):         serializer_context = {'request': self.context.get('request') }         children = Child.objects.all().filter(parent=obj)         serializer = ChildSerializer(children, many=True, context=serializer_context)         return serializer.data 

and in my CustomModelSerializer:

class CustomModelSerializer(rest_serializer_classes.HyperlinkedModelSerializer):      def __init__(self, *args, **kwargs):         """             Make sure a user is coupled to the serializer (needed for permissions)         """         super().__init__(*args, **kwargs)         if not self.context:             self._context = getattr(self.Meta, 'context', {})         try:             self.user = self.context['request'].user         except KeyError:             self.user = None       def get_fields(self):         ret = OrderedDict()          if not self.user:             print("No user associated with object")             return ret          fields = super().get_fields()          # Bypass permission if superuser         if self.user.is_superuser:             return fields          for f in fields:             if has_right(self.user, self.Meta.model.__name__.lower(), f, "read"):                 ret[f] = fields[f]          return ret 

This seems to work fine, and fields of the child are discarded in the serializer when i either revoke read-rights on Child.c_name or on Parent.child

Answer 2

If you can not change the nature of you child serializer, as in @Kirill Cherepanov and @Robin van Leeuwen answers, a light but not full-integrated solution would be to manually pass the context in __init__() function :

class ChildSerializer(CustomModelSerializer):     class Meta:         fields = ('c_name', )         model = Child   class ParentSerializer(CustomModelSerializer):      child = ChildSerializer(many=True, read_only=True)      class Meta:         model = Parent         fields = ('p_name', 'child')      def __init__(self, *args, **kwargs):         super().__init__(*args, **kwargs)         # We pass the "upper serializer" context to the "nested one"         self.fields['child'].context.update(self.context)