model_serializer.py

class ModelSerializer(Serializer):
  def update(self, instance, validated_data):
        raise_errors_on_nested_writes('update', self, validated_data)
        info = model_meta.get_field_info(instance)

        # Simply set each attribute on the instance, and then save it.
        # Note that unlike `.create()` we don't need to treat many-to-many
        # relationships as being a special case. During updates we already
        # have an instance pk for the relationships to be associated with.
        m2m_fields = []
        for attr, value in validated_data.items():
            if attr in info.relations and info.relations[attr].to_many:
                m2m_fields.append((attr, value))
            else:
                setattr(instance, attr, value)

        instance.save(update_fields=list(validated_data.keys()))  # This is the modified line on the model serializer

        # Note that many-to-many fields are set after updating instance.
        # Setting m2m fields triggers signals which could potentially change
        # updated instance and we do not want it to collide with .update()
        for attr, value in m2m_fields:
            field = getattr(instance, attr)
            field.set(value)

        return instance