Django Rest Framework serializer update method does not save object

Question

I have overridden the update method for one of my serializers to call a model's method before saving the object. Like so:

class MyModelSerializer(serializers.ModelSerializer):
    class Meta:
        model = MyModel
        fields = [...]

    def update(self, instance, validated_data):
        instance.model_method()
        instance.save()
        return instance

In my views, I am saving the serializer using serializer.save(), and of course setting it using MyModelSerializer(instance, data=request.data). However, my instance is not being saved. Just removing the update method saves the instance, but does not call the model_method() obviously. How can I fix this issue? Thanks for any help.

What does the model_method do? Does it modify any attributes of the instance? — Rahul Gupta
– Rahul Gupta, Commented Nov 9, 2019 at 6:32
Did you try returning super() call at the end ie after 1st line instead of calling instance.save(). — Rahul Gupta
– Rahul Gupta, Commented Nov 9, 2019 at 15:50

Rahul Gupta · Accepted Answer · 2019-11-10 07:08:27Z

10

You need to call super() method after instance.model_method() is called so as to save the data on the updated instance.

The problem with the approach mentioned above in the question is that validated_data is not used anywhere to save() which leaves the instance as is.

class MyModelSerializer(serializers.ModelSerializer):
    class Meta:
        model = MyModel
        fields = [...]

    def update(self, instance, validated_data):
        instance.model_method() # call model method for instance level computation

        # call super to now save modified instance along with the validated data
        return super().update(instance, validated_data)

answered Nov 10, 2019 at 7:08

Rahul Gupta

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