How to fetch all records from 2 tables - django

Question

I have 2 models
class CustomUser(AbstractBaseUser, PermissionsMixin):
email = models.EmailField(unique=True)
employee_id = models.CharField(max_length=13, unique=True)
class UserRole(models.Model):
employee_id = models.ForeignKey(CustomUser, to_field='employee_id', unique=True, on_delete=models.CASCADE)
supervisor_id = models.CharField(max_length=20, null=True)
and have defined seriallizers for both models
class UserSerializer(serializers.ModelSerializer):
class Meta:
fields = '__all__'
model = models.CustomUser
class UserRoleSerializer(serializers.ModelSerializer):
class Meta:
fields = '__all__'
model = models.UserRole
consider i have 5 records in both tables
How to fetch all records from both tables (email, employee_id, supervisor_id )
like, where CustomUser.employee_id = UserRole.employee_id
I tried with
models.CustomUser.objects.select_related('UserRole')
But, not able to fetch records from UserRole table.
UserRole.objects.select_related('employee_id')
-- this is fetching only userRole records
Thanks in Advance

Answer 1

You don't get automatic joins in Django, no need for it because you can just follow the ForeignKey relation on the object (the_object_you_get.its_foreign_key). Now, of course, that will hit the DB twice. if you'd rather avoid that, you can use something like .prefetch_related('employee_id') on whatever queryset you need to use. This will prevent you from hitting the DB multiple times (at the price of one larger initial query of course).
Finally, if you wanna serialize a ForeignKey relation, the answer Shakil gave is pretty comprehensive. Only thing is that you don't necessarily need to set the employee_id field as read_only=True (a bit of a limitation). You can also override the UserRoleSerializer .create() the method so that it calls the .create() method of UserSerializer.

Answer 2

I think from UserRole you want to all information about employe's too. What i am thinking you want to get all details information of employee_id foreign_key relation. This can be done by
UserRole.objects.all()
with the following serializers.
class UserSerializer(serializers.ModelSerializer):
class Meta:
fields = ('email','employee_id',)
model = models.CustomUser
class UserRoleSerializer(serializers.ModelSerializer):
employee_id = UserSerializer()
class Meta:
fields = ('employee_id','supervisor_id',)
model = models.UserRole