Count the number of objects in another model - django

Question

I have two models in different apps: Program in programs and Contact in contacts. Each program can have many contacts. I want to have a field in Program called database_quantity that shows how many contacts are associated with that program. Here is what I have tried so far which is giving me this error: ImportError: cannot import name 'Contact'. I think this has to do with circular referencing but I am lost with how to proceed.
programs models.py
from django.db import models
from django.utils import timezone
from django.contrib.auth.models import User
from contacts.models import Contact
class Program(models.Model):
program_code = models.CharField(max_length=6)
program_format = models.ForeignKey(ProgramFormat, models.SET_NULL, blank=True, null=True)
program_type = models.ForeignKey(ProgramType, models.SET_NULL, blank=True, null=True)
program_board = models.ForeignKey(RealEstateBoard, models.SET_NULL, blank=True, null=True)
article_content_type = models.ForeignKey(ArticleContentType, models.SET_NULL, blank=True, null=True)
program_name = models.CharField(max_length=60)
date_created = models.DateTimeField(default=timezone.now)
client = models.ForeignKey(User, on_delete=models.CASCADE)
def get_database_quantity(self):
database_quantity = Contact.objects.all().filter(Contact.author=Program.client)
return database_quantity
database_quantity = property(get_database_quantity)
contacts models.py
from django.db import models
from django.utils import timezone
from django.contrib.auth.models import User
from django.urls import reverse
from programs.models import Program
class Contact(models.Model):
first_name1 = models.CharField(max_length=100, verbose_name='First Name')
last_name1 = models.CharField(max_length=100, verbose_name='Last Name', blank=True)
date_posted = models.DateTimeField(default=timezone.now)
author = models.ForeignKey(User, on_delete=models.CASCADE)
active_status = models.BooleanField(default=True)
program_code = models.ForeignKey(Program, on_delete=models.DO_NOTHING, null=True, blank=True)
Settings Installed Apps
INSTALLED_APPS = [
'blog.apps.BlogConfig',
'users.apps.UsersConfig',
'contacts.apps.ContactsConfig',
'programs.apps.ProgramsConfig',
'crispy_forms',
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'import_export',
]
contacts apps.py
from django.apps import AppConfig
class ContactsConfig(AppConfig):
name = 'contacts'

Answer 1

1- You can define your ForeignKey mappings with strings instead of Model references, like this:
program_code = models.ForeignKey('programs.Program', on_delete=models.DO_NOTHING, null=True, blank=True)
So that you won't need to import a model from another app into models.py
2 - You have several problems in your get_database_quantity method, you need to filter with model instance, not model Class, i.e self.client instead of Program.client. Also you shouldn't filter like Contact.author=..., it should be like author=.... And, to get quantity, you need .count() method of querysets. Finally, you can import other model locally to avoid circular import issues.
def get_database_quantity(self):
from contacts.models import Contact
database_quantity = Contact.objects.filter(author=self.client).count()
return database_quantity
3 - You can also write get_database_quantity like this:
def get_database_quantity(self):
return self.client.contacts.count()
If you define your related ForeignKey field like this:
author = models.ForeignKey(User, on_delete=models.CASCADE, related_name='contacts')