CODEWITHSUNDEEP
pythondjango
Fermin Arellano
Fermin Arellano

Reputation: 633

Django Generic Relations not working

So, after adding or removing a GenericRelation to one of my model classes nothing happens.

I try to makemigrations and it tells me no changes were detected. So there must be something wrong, because it should be hitting the database and try to apply some changes.

I followed Django example and I can't make the relationship work. 

class Person(models.Model):
    identity = models.CharField(max_length=13, verbose_name="ID")
    name = models.CharField(max_length=255, verbose_name="Name")
    board = GenericRelation('second_app.BoardMember') #Second Try

    def __unicode__(self):
        return self.identity

    class Meta:
        verbose_name = "Person"
        verbose_name_plural = "People"

class Student(Person):
    class Meta:
        proxy = True

class Parent(Person):
    class Meta:
        proxy = True

class Teacher(Person):
    board = GenericRelation('second_app.BoardMember') # first try
    class Meta:
        proxy = True

On a different app I have the following model.

class BoardMember(models.Model):
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id', for_concrete_model=False)
    responsabilities = models.CharField(max_length=255)

At first I tried setting the Generic Relation on a proxy model. Nothing happened, then I tried setting it on the main Person class. Nothing. This is what I did to test the relation on the shell. 

>>>from first_app.models import Teacher
>>>from second_app.models import BoardMember
>>>teacher = Teacher(identity='123456', name='Fermin Arellano')
>>>teacher.save()
>>>bm = Boardmember(content_object=teacher,responsabilities='Check stuff')
>>>bm.save()
>>>teacher.board.all()
[]

Following this example: https://docs.djangoproject.com/en/1.8/ref/contrib/contenttypes/#reverse-generic-relations

The expected result should be: [<Teacher: 123456>]

Am I doing something wrong? There are no errors showing anywhere. Data is saved properly, both the Teacher and BoardMemer objects were created successfully in my database.

Upvotes: 2

Views: 980

Answers (1)

Fermin Arellano
Fermin Arellano

Reputation: 633

I just removed for_concrete_model=False from the GenericForeignKey declaration. Although on Django´s documentation it clearly states that it has to be setted to false in order to use ProxyModels.

Everythings is working fine now.

EDIT.

I just realized that the problem persists. After further investigation I noticed that in order to get the generic relation to work I need to save the content_type_id of the Person model, and not the proxy one. That is why deleting the for_concrete_model parameter helped, because this way I told Django to use the parents content type, and there it worked fine. Funny thing is that if I do the following the relations still works eventhough I have the content_type_id of Person.

Teacher.objects.filter(board__isnull=False)

This returns all the teachers who are in the board.

This is really confusing, if you can shed some light on this mess I'll be very thankful.

Upvotes: 1

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