Validate across nested serializers with django rest framework

Question

If you were to have a nested serializer, but required a certain parameter in the parent depending on a value in the child, how could you enforce the logical requirement when necessary?

For example:

class ChildSerializer(serializers.ModelSerializer):
     foobar_attribute = serializers.ChoiceField(
         required=True,
         choices=foobar_choices,
     )



class ParentSerializer(serializers.ModelSerializer):
     child = ChildSerializer(required=True)

     optional_attribute = serializers.CharField(
         required=False,
     )

optional_attribute should be required only when foobar_attribute is a certain choice, but optional for all else. Throwing a validate function on ParentSerializer or ChildSerializer only exposes attributes for that serializer, and none else.

How can I perform validation across nested serializers without creating rows ( as would occur if validation was performed in perform_create )?

have you tried to override the validate method of ParentSerializer ? — JPG
– JPG, Commented Dec 3, 2019 at 18:18
Yes, the values of the child are not surfaced with validate on the parent — arshbot
– arshbot, Commented Dec 3, 2019 at 18:21

Ignacio Villela · Accepted Answer · 2019-12-03 18:29:13Z

1

You can overwrite the __init__ function

def __init__(self, instance=None, *args, **kwargs):
    super().__init__(instance, *args, **kwargs)
    if your_condition:
        self.fields['optional_attribute'].required = True

You can also change any attribute of the optional_attribute field

answered Dec 3, 2019 at 18:29

Ignacio Villela

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2 Comments

JPG Over a year ago

your_condition is something should fetch from the input data

JPG Over a year ago

valid one. IMHO, it's better to implement validation logic inside the validators or something similar

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