serialization - Is serializer field level validation called if initial_data does not have a key for that field name?

Question

data = {...}

MySerializer(serializers.Serializer):
  ...
  def validate_[my_field_name]()
     ...

The data dictionary does not contain the key my_field_name

Then will the validate_[my_field_name]() method be called when I call

serializer = MySerializer(data=data)
serializer.is_valid()

Answer 1

Sadly, No.

This is something that causes me pain, fairly often too. There are a few things you can do:

• Set required=True when you declare your field
• Supply a default=, if that is sufficient

The validate method of the serializer is always called, and you can add something in there if you want to

class A(Serializer):
   
    must_send = serializers.CharField(required=True)
    
 
    def validate(self, attrs):
        if 'key' not in attrs:
            attrs.setdefault('key', some_calculation())

        # important!
        return attrs