Django GenericRelation fields not available during South migration

问题

In a Django project, I have models defined like this :

from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic

class TaggedEntry(models.Model):
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey("content_type", "object_id")

    class Meta:
        abstract = True

class File(TaggedEntry):
    name = models.CharField(max_length = 256)
    # some more fields

class Folder(models.Model):
    name = models.CharField(max_length = 200)
    files = generic.GenericRelation(File)
    # some more fields

In the project I can use them this way :

folder = Folder.objects.get(name="fooo")
for f in folder.files.iterator():
    print f.name

I'm now preparing a datamigration with South in which I need to access the files of the folders but the code folder.files.iterator()

gives me an error :

Error in migration: main:0015_contenttype_to_manytomany_step0
AttributeError: 'Folder' object has no attribute 'files'

Is it expected?

How can I know the files being part of a folder?

回答1:

I've found a workaround filtering File's object with the appropriate content_type_id and object_id:

from django.contrib.contenttypes.models import ContentType
# ...
folder_contenttype = ContentType.objects.get(name="folder")
for folder in orm.Folder.objects.all():
    for f in orm.File.objects.filter(content_type_id = folder_contenttype.id, object_id = folder.id): # replaces folder.files.iterator():
        # ...

This works but is less readable.

来源：https://stackoverflow.com/questions/21759146/django-genericrelation-fields-not-available-during-south-migration