Django How to link a foreign key to many tables

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I have n classes and each class contains a column called key like this (where n==3)

class class1(models.Model):
    Id1 = models.AutoField(primary_key=True)
    key = models.CharField(max_length = 16, blank=True)

class class2(models.Model):
    Id2 = models.AutoField(primary_key=True)
    key = models.CharField(max_length = 16, blank=True)

class class3(models.Model):
    Id3 = models.AutoField(primary_key=True)
    key = models.CharField(max_length = 16, blank=True)

I want to make the column key as Foreign key between all the n classes? I know how make a foreign key between 2 classes but I want to do that with many classes because I have about 40 classes and some classes has some commun columns

django python
1 Answers

You can use generic relations to make a Foreign Key to a generic model. You need to use the ContentType framework, write your models like:

from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
from django.db import models

class class1(models.Model):
    Id1 = models.AutoField(primary_key=True)
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

class class2(models.Model):
    Id2 = models.AutoField(primary_key=True)
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

Then when you create a class1 instance, you could make a Foreign Key to a class2 (or another model) instance with:

class1_instance = class1.objects.create(content_object=class2.objects.get(id2=1))

Then you can access the class2 instance with:

class1_instance.content_object
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