Django REST Framework: SlugRelatedField for indirectly-related attribute?

Question

I have a Profile model that has a one-to-one relationship with Django's User model, and I have another model, called Permission (unrelated to Django's internal idea of permissions), that has a foreign key to Profile. Like this: (I've removed most of the fields here, for simplicity)

from django.db import models
from django.contrib.auth.models import User as DjangoUser

class Account(models.Model):
    name = models.CharField(max_length=200, db_index=True)

class Profile(models.Model):
    django_user = models.OneToOneField(DjangoUser)
    default_account = models.ForeignKey(Account)

class Permission(models.Model):
    # Which user has the permission
    user = models.ForeignKey(Profile, db_index=True)
    # Which account they have the permission on
    account = models.ForeignKey(Account, db_index=True)

I want to make a serializer for Permission, that will create objects like this:

{
  "user": "[email protected]",
  "account": 123
}

where the value of "account" is the account's primary key (so that's easy, I can use a PrimaryKeyRelatedField) and the value of "user" is the user's email address (this is the part I haven't figured out yet, because the email address is not stored directly on the Profile object, it's on the associated DjangoUser object). Note also that this is NOT read-only - when creating a Permission it does need to be able to deserialize from an email address to a Profile object.

Some things I have tried so far, for representing the user on the Permission serializer ...

1.

user = serializers.RelatedField(read_only=False)

With this one, if I POST an email address (or primary key or anything else) as the "user", it returns a 400 error saying {"user": "This field is required."}, as if I didn't include the field at all.

2.

user = serializers.SlugRelatedField(slug_field='django_user.email')

With this one, I get AttributeError: 'Profile' object has no attribute 'django_user.email'. Same thing happens if I use 'django_user__email'.

Any ideas?

Answer 1

According to Django REST Framework serializer reference (http://www.django-rest-framework.org/api-guide/fields/#core-arguments):

The name of the attribute that will be used to populate the field. May be a method that only takes a self argument, such as URLField(source='get_absolute_url'), or may use dotted notation to traverse attributes, such as EmailField(source='user.email').

So, if source='user.email' is not working, you can try to create a method (e.g. get_user_email), use it in source field and make it return the user email manually.