Django reverse foreignkey relationship failing - django

Question

I have set up two models where one has a foreign key relationship to the other. Since I have multiple databases I also set up a routers.py file as both databases live in the same application. I have been reading and following the documenation found here and here and as far as I can tell I am following the documentation to the letter.
models.py
class Customers(models.Model):
customer_id = models.AutoField(primary_key=True)
name = models.CharField(max_length=100)
active = models.IntegerField()
class Meta:
db_table = 'customers'
app_label = 'db1'
class Users(models.Model):
user_id = models.AutoField(primary_key=True)
customer = models.ForeignKey(Customers, models.CASCADE)
username = models.CharField(max_length=35)
role = models.ForeignKey(Roles, models.CASCADE)
active = models.IntegerField()
class Meta:
db_table = 'users'
app_label = 'db1'
routers.py
class BackendRouter(object):
def db_for_read(self, model, **hints):
if model._meta.app_label == 'db1':
return 'default'
elif model._meta.app_label == 'db2':
return 'db2'
return None
def db_for_write(self, model, **hints):
if model._meta.app_label == 'db1':
return 'default'
elif model._meta.app_label == 'db2':
return 'db2'
return None
def allow_relation(self, obj1, obj2, **hints):
if obj1._meta.app_label == 'db1' or \
obj2._meta.app_label == 'db1':
return True
elif obj1._meta.app_label == 'db2' or \
obj2._meta.app_label == 'db2':
return True
return None
def allow_migrate(self, db, app_label, model_name=None, **hints):
if app_label == 'db1':
return db == 'default'
elif app_label == 'db2':
return db == 'db2'
return None
Ignore for a second that I have a users table without deriving from AbstractBaseUser, when I run the following query:
Customers.objects.filter(users__username__contains='sl')
I get the following error:
django.core.exceptions.FieldError: Cannot resolve keyword 'users' into
field. Choices are: active, customer_id, name
Per the example in the documentation:
Blog.objects.filter(entry__headline__contains='Lennon')
This should work. What am I missing here?
As a point of reference I have already tried the following as well:
Customers.objects.filter(users_set__username__contains=‘sl’)
As well as setting related_name='users' on the customers ForeignKey.

Answer 1

Based on the docs, it seems I should be able to filter the way I have in my question and not run into an issue. However I am not sure if I can actually filter on more than a single object when doing "reverse" relations. I did achieve what I wanted with the following solution:
user = Users.objects.filter(username='someuser').only('customer_id')
customer = Customers.objects.filter(customer_id__in=user)
I am sure there is a more efficient way though. Like such:
Users.objects.filter(username='someuser').values_list('customer__name', flat=True)[0]
I just figured it would be better if I could get what I need via something like:
Customers.objects.filter(users__username='someuser').values_list('name', flat=True)[0]
It actually appears that this was caused by both of my models living in the same application. Once I split them out into there own seperate apps, reverse relationships began to work.