Usage of .to_representation() and .to_internal_value in django-rest-framework?

Question

What do .to_representation() and .to_internal_value do in serializers?
If I pass data to a serializer, is the data thrown to_representation() first?
What's the usage of these two?

Answer 1

If you want to create a custom field, you'll need to subclass Field and then override either one or both of the .to_representation() and .to_internal_value() methods. These two methods are used to convert between the initial datatype, and a primitive, serializable datatype. Primitive datatypes will typically be any of a number, string, boolean, date/time/datetime or None. They may also be any list or dictionary like object that only contains other primitive objects. Other types might be supported, depending on the renderer that you are using.

The .to_representation() method is called to convert the initial datatype into a primitive, serializable datatype.

The to_internal_value() method is called to restore a primitive datatype into its internal python representation. This method should raise a serializers.ValidationError if the data is invalid.

Note that the WritableField class that was present in version 2.x no longer exists. You should subclass Field and override to_internal_value() if the field supports data input.

Ref:

1. http://www.django-rest-framework.org/api-guide/fields/#custom-fields
2. https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/serializers.py#L417