How do I get a value from a different model in django? - django

Question

Im new to django and im trying to figure out how to set the value in a model = to a value in another model
from django.db import models
from django.contrib.auth.models import User
class Company(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE, null=True)
name = models.CharField(max_length=100, null=True, blank=True) # This is the value I want
_id = models.AutoField(primary_key=True, editable=False)
def __str__(self):
return self.name
class Product(models.Model):
company = models.ForeignKey(Company, on_delete=models.CASCADE, null=True)
companyName = # I want the name here
_id = models.AutoField(primary_key=True, editable=False)
def __str__(self):
return self.name
I've tried these but they dont work
companyName = Company.name
companyName = models.CharField(Company.name, max_length=100, null=True, blank=True)

Answer 1

Company.name will not work because Company is a class, a template for making many Company objects, each with it's own name, so which Company object, or instance, do you want?
You need to get the particular Company first, and then you can set the companyName of the Product, or, you can set it when you save the Product instance, assuming you have a Company instance in mind, since you set null=True, so obviously if company is False, then there is no companyName.
Assuming you have a Company instance already when you save the Product model you can do:
class Product(models.Model):
company = models.ForeignKey(Company, on_delete=models.CASCADE, null=True)
companyName = # I want the name here
_id = models.AutoField(primary_key=True, editable=False)
def save(self, *args, **kwargs):
if self.company:
self.companyName = self.company.name
super(Product, self).save(*args, **kwargs)
def __str__(self):
return self.name
But, the next question is why do you want to even have a field called companyName when you have access to the name field of the Company instance anyway. Try to get it by:
# Get the Product instance you want
product = Product.objects.get(...)
# Then you can get the associated `Company` name like this:
print(product.company.name)
Suggestion
Lately I've been seeing many questions with something like:
_id = models.AutoField(primary_key=True, editable=False)
Not sure why, since Django does that automatically.