Django query using related_name through another related_name - django

Question

I have several models that have a ForeignKey back to a model which has a ForeignKey back to auth User in Django.
models.py
class UserDetails(models.Model):
user = models.ForeignKey(
settings.AUTH_USER_MODEL,
related_name='userdetail_related')
details = models.CharField(max_length=100)
email = models.EmailField(unique=True)
class UserInformation(models.Model):
user = models.ForeignKey(
UserDetails,
related_name='userinfo_related')
info = models.CharField(max_length=100, default='this')
EDIT
My actual code for related_name as per Django Documentation is: related_name='%(app_label)s_%(class)s_related'. I put 'userdetail_related' for ease of explanation here.
Only one UserDetail per User, but many UserInformation per UserDetail.
Where there is an unregistered user and we have captured their email, the email can have UserDetail and UserInformation associated with it for a shopping cart guest checkout system.
In my View I want to access the UserInformation model from self.request.user.
I can access UserDetails in my view via:
details = self.request.user.userdetail_related.filter(
user=self.request.user).first()
But I can't seem to access UserInformation via:
info = self.request.user.userdetail_related.filter(
user=self.request.user).first().userinfo_related.filter(
info='this').first()
The only way I can get this to work is:
details = self.request.user.userdetail_related.filter(
user=self.request.user).first()
info = details.userinfo_related.filter(
info='this').first()
But this surely hits the database twice which I don't want.
Does anyone have a better way of getting the info from UserInformation using the session user 'through' UserDetails?

Answer 1

You can use following:
user_info = UserInformation.objects.filter(user__user=self.request.user).first()
Additionally, when you access UserDetails you don't really need the filter since you are trying to access the related objects from the user itself. So following would work as well.
details = self.request.user.userdetail_related.first()
And as a side note, I think you need OneToOneField here since one user should have only one UserDetails.

Answer 2

As it suggested by #AKS you should use OneToOneField to connect your models to the User. You can do it like this:
class UserDetails(models.Model):
user = models.OneToOneField(
settings.AUTH_USER_MODEL,
related_name='userdetail_related')
details = models.CharField(max_length=100)
class UserInformation(models.Model):
user = models.OneToOneField(
UserDetails,
related_name='userinfo_related')
info = models.CharField(max_length=100, default='this')
Then you can access UserInformation and UserDetails like this:
details = self.request.user.userdetail_related.details
info = self.request.user.userinfo_related.info

Answer 3

To add to the other answers, a few remarks about the layout.
For Model names, best to always use singular (UserDetails -> UserDetail), not plural. Then, for the related name of a ForeignKey, use the plural (because the reverse lookup may find more than one item that have the backwards relationship).
class UserDetail(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='details')
details = models.CharField(max_length=100)
class UserInformation(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='info')
info = models.CharField(max_length=100, default='this')
Makes it much simpler to access in the views
request.user.infos.all().first()
request.user.details.filter(info__startswith="something")
Also, if practical, add both onto the User object, because "flat is better than nested" .
If every User only has one UserDetail and one UserInformation then its best to use OneToOneFields instead.