I have the following models example:

class TestSet(models.Model):
    name = models.CharField(max_length=50)

    def __str__(self):
        return self.name

class Class(models.Model):
    name = models.CharField(max_length=50)
    test_set_id = models.ForeignKey(TestSet)

    def __str__(self):
        return self.name

class Test(models.Model):
    title = models.CharField(max_length=50)
    test_set_id = models.ForeignKey(TestSet)

    def __str__(self):
        return self.title

class ClassTest(models.Model):
    class_id = models.ForeignKey(Class)
    test_id = models.ForeignKey(TestSet)
    memo = models.CharField(max_length=250)

    def __str__(self):
        return self.memo

What I want to do is when a new Class or Test is created, it should also create automatically a ClassTest entry if their test_set_id matches with the currenct entries on the database.

Example:

1. Lets say I already have three Test objects with test_set_id = 1
2. I create a new Class object with test_set_id = 1
3. After creating the new Class object, the program should also create 3 new entries in the ClassTest model connecting classes to tests based on the match of the test_set_id field.
4. It should work the same if a new Test object is added.