#36135: Prefetch GenericForeignKey with ManyToMany field error
--------------------------+-----------------------------------------
Reporter: john | Type: Bug
Status: new | Component: Uncategorized
Version: 5.1 | Severity: Normal
Keywords: prefetch | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
--------------------------+-----------------------------------------
I have some models in my app:
{{{
class User(models.Model):
name = models.CharField()
class Project(models.Model):
name = models.CharField()
users = models.ManyToManyField('User', related_name='projects')
class Task(models.Model):
name = models.CharField()
project = models.ForeignKey('Project', on_delete=models.DO_NOTHING,
related_name='tasks', null=True)
link_entity_type = models.ForeignKey(ContentType,
on_delete=models.DO_NOTHING, null=True, related_name='link_tasks')
link_entity_id = models.IntegerField(null=True)
link = GenericForeignKey('link_entity_type', 'link_entity_id')
class Version(models.Model):
name = models.CharField()
task = models.ForeignKey('Task', on_delete=models.DO_NOTHING,
related_name='versions', null=True)
class Shot(models.Model):
name = models.CharField()
users = models.ManyToManyField('User', related_name='shots')
link_tasks = GenericRelation(
'Task',
object_id_field='link_entity_id',
content_type_field='link_entity_type'.format(field.name),
related_query_name='link_Shot'
)
class Asset(models.Model):
name = models.CharField()
users = models.ManyToManyField('User', related_name='assets')
link_tasks = GenericRelation(
'Task',
object_id_field='link_entity_id',
content_type_field='link_entity_type'.format(field.name),
related_query_name='link_Asset'
)
}}}
If I query Task and prefetch project and users, I will use:
{{{
query = Task.objects.all().prefetch_related('project__users')
for i in query:
print(i.id)
}}}
This is ok, I can get the result.
But if I want to query Task and prefetch link_Shot and users
{{{
query = Task.objects.all().prefetch_related('link_Shot__users')
for i in query:
print(i.id)
}}}
or
{{{
query = Version.objects.all().prefetch_related('task__link_Shot__users')
for i in query:
print(i.id)
}}}
I got error:
{{{
Traceback (most recent call last):
File "/ela/workspace/xinghuan/issues/sins/sins2server/tmp/tst_query.py",
line 35, in <module>
for i in query:
File
"/UNC/fs_user_ws.ela.com/ela/workspace/xinghuan/issues/sins/sins2server/tmp/django/db/models/query.py",
line 398, in __iter__
self._fetch_all()
File
"/UNC/fs_user_ws.ela.com/ela/workspace/xinghuan/issues/sins/sins2server/tmp/django/db/models/query.py",
line 1883, in _fetch_all
self._prefetch_related_objects()
File
"/UNC/fs_user_ws.ela.com/ela/workspace/xinghuan/issues/sins/sins2server/tmp/django/db/models/query.py",
line 1273, in _prefetch_related_objects
prefetch_related_objects(self._result_cache,
*self._prefetch_related_lookups)
File
"/UNC/fs_user_ws.ela.com/ela/workspace/xinghuan/issues/sins/sins2server/tmp/django/db/models/query.py",
line 2321, in prefetch_related_objects
obj_list, additional_lookups = prefetch_one_level(
File
"/UNC/fs_user_ws.ela.com/ela/workspace/xinghuan/issues/sins/sins2server/tmp/django/db/models/query.py",
line 2463, in prefetch_one_level
) = prefetcher.get_prefetch_queryset(instances,
lookup.get_current_queryset(level))
File
"/UNC/fs_user_ws.ela.com/ela/workspace/xinghuan/issues/sins/sins2server/tmp/django/db/models/fields/related_descriptors.py",
line 746, in get_prefetch_queryset
instance = instances_dict[rel_obj_attr(rel_obj)]
File
"/UNC/fs_user_ws.ela.com/ela/workspace/xinghuan/issues/sins/sins2server/tmp/django/db/models/fields/related.py",
line 750, in get_local_related_value
return self.get_instance_value_for_fields(instance,
self.local_related_fields)
File
"/UNC/fs_user_ws.ela.com/ela/workspace/xinghuan/issues/sins/sins2server/tmp/django/db/models/fields/related.py",
line 772, in get_instance_value_for_fields
ret.append(getattr(instance, field.attname))
AttributeError: 'Shot' object has no attribute 'link_entity_id'
}}}
The discussion link:
[https://forum.djangoproject.com/t/how-to-prefetch-a-genericforeignkey-
with-manytomany-field/38168]
I'm using Django 4.2.16 and python 3.9.
I also tried Django 5.1.5 and python 3.10 and the error is same.
--
Ticket URL: <https://code.djangoproject.com/ticket/36135>
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