Django ORM: Join two tables using a linked table - django

Question

I want to integrate a function has_permission(self, permission_name) in the class Profile.
For this I want to do make a ORM statement which returns a list of permission names.
The data model is:
1 User has 1 Profile (extends Django's User model)
Each Profile is assigned to one ProfileGroup.
However, different Profiles can belong to the same ProfileGroup.
Each ProfileGroup can have one or more ProfilePermissions. Groups can have the same subsets of ProfilePermissions. The Link-Table GroupPermissions handles this using two ForeignKeys instead of a ManyToMany relation.
My models.py looks like this:
class ProfileGroup(models.Model):
name = models.CharField(max_length=64)
class ProfilePermission(models.Model):
name = models.CharField(max_length=64)
class GroupPermissions(models.Model):
group = models.ForeignKey(ProfileGroup, on_delete=models.RESTRICT)
permission = models.ForeignKey(ProfilePermission, on_delete=models.RESTRICT)
class Meta:
constraints = [
models.UniqueConstraint(fields=['group', 'permission'], name='Unique')
]
def __str__(self):
return f'Group "{self.group.name}" has permission "{self.permission.name}"'
class Profile(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
group = models.ForeignKey(ProfileGroup, on_delete=models.RESTRICT)
def __str__(self):
return f'Profile of {self.user.username}'
def has_permission(self, permission_name):
return True
The function has_permission (in the Profile class) should check if the permission permission is included in the list of Permissions. I tried it with
list_of_permissions = GroupPermissions.objects.filter(group=self.group)
But this returns a list of ProfilePermission. What I want is a list of names of the permission (permission.name).
So I have to join the two Tables GroupPermissions and ProfilePermission. I found things as prefetch_related and select_related but this does not work as I want.

Answer 1

Answering your question directly,
class Profile(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
group = models.ForeignKey(ProfileGroup, on_delete=models.RESTRICT)
def __str__(self):
return f'Profile of {self.user.username}'
def has_permission(self, permission_name):
return GroupPermissions.objects.filter(group=self.group, permission__name=permission_name).exists()
But... My advice to you is to not try to reinvent the wheel. django.contib.auth has already groups and permissions, just use them ;-)