Bump?
Almost exactly 4 years later, I've ran into this exact same issue in Django
1.4. Attempting to use get_or_create through a ManyToMany field results in
an integrity error if the object already exists but is not yet associated
with the parent object. To use the OP's example, if a Tag with name "foo"
exists but is not yet associated with a given Thing instance, using
.tags.get_or_create(name='foo') will indeed raise an IntegrityError:
foo_tag = Tag(name='foo')
foo_tag.save()
a_thing = Thing(name='a')
a_thing.save()
a_thing.tags.get_or_create(name='foo')
Traceback (most recent call last):
File "", line 1, in
File
"/usr/local/lib/python2.7/dist-packages/django/db/models/fields/related.py",
line 616, in get_or_create
super(ManyRelatedManager, self.db_manager(db)).get_or_create(**kwargs)
File
"/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py", line
134, in get_or_create
return self.get_query_set().get_or_create(**kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py",
line 449, in get_or_create
obj.save(force_insert=True, using=self.db)
File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py",
line 463, in save
self.save_base(using=using, force_insert=force_insert,
force_update=force_update)
File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py",
line 551, in save_base
result = manager._insert([self], fields=fields, return_id=update_pk,
using=using, raw=raw)
File
"/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py", line
203, in _insert
return insert_query(self.model, objs, fields, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py",
line 1576, in insert_query
return query.get_compiler(using=using).execute_sql(return_id)
File
"/usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py",
line 910, in execute_sql
cursor.execute(sql, params)
File "/usr/local/lib/python2.7/dist-packages/django/db/backends/util.py",
line 40, in execute
return self.cursor.execute(sql, params)
File
"/usr/local/lib/python2.7/dist-packages/django/db/backends/sqlite3/base.py",
line 337, in execute
return Database.Cursor.execute(self, query, params)
IntegrityError: column name is not unique
I've traced the problem to being that the ManyRelatedManager includes its
core_filters in its get_query_set method. This results in the "get" portion
of get_or_create to only return a hit if the Tag exists and is already
associated to the calling Thing instance. Given the nature of a
many-to-many relationship, it should not be a requirement that a Tag
already be linked to the calling Thing for get_or_create to find it; it
should be enough that the Tag simply exists. All that should happen in that
scenario is that the (existing) Tag's relationship with the calling Thing
be created/saved.
On Monday, September 1, 2008 8:04:00 PM UTC-7, Cap wrote:
>
> I'm having problems using get_or_create with a ManyToManyField and I'm
> not sure whether the problem is me or Django.
>
> I have two models:
>
> class Tag(models.Model):
> name = models.CharField(max_length=256, unique=True)
>
> class Thing(models.Model):
> name = models.CharField(max_length=256)
> tags = models.ManyToManyField(Tag)
>
> When I try to add a tag that already exists, as:
>
> a = Thing(name='a')
> a.save()
> a.tags.get_or_create(name='foo')
>
> I get sqlite3.IntegrityError: column name is not unique.
>
> But when I do it like so:
>
> a = Thing(name='a')
> a.save()
> foo, created = Tag.objects.get_or_create(name='foo')
> a.tags.add(foo)
>
> I have no problems.
>
> I noticed that http://code.djangoproject.com/ticket/3121 seemed to
> address something like this, so I pulled the latest Django (8834), but
> the problems remains.
>
> Am I doing it wrong?
>
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