Opened 11 years ago

Closed 9 years ago

Last modified 6 years ago

#3121 closed defect (fixed)

RelatedManager.get_or_create() does not work

Reported by: Antti Kaihola Owned by: Gary Wilson
Component: Database layer (models, ORM) Version: master
Severity: normal Keywords:
Cc: christoph.neuroth@… Triage Stage: Accepted
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: UI/UX:


Given the following models:

class Poll(models.Model):
    question = models.CharField(maxlength=200)
    pub_date = models.DateTimeField('date published')

class Choice(models.Model):
    poll = models.ForeignKey(Poll)
    choice = models.CharField(maxlength=200)
    votes = models.IntegerField()

you can do:

>>> what, created = Poll.objects.get_or_create(question='What?', pub_date='2006-12-09')
>>> django = what.choice_set.create(choice='Django', votes=100)
>>> python, created = Choice.objects.get_or_create(poll=what, choice='Python', votes=200)

But for some reason this doesn't work:

>>> php, created = what.choice_set.get_or_create(choice='PHP', votes=1)

but gives the following error and traceback:

<class 'sqlite3.IntegrityError'> Traceback (most recent call last)

django/db/models/ in get_or_create(self, **kwargs)
     69     def get_or_create(self, **kwargs):
---> 70         return self.get_query_set().get_or_create(**kwargs)
     72     def create(self, **kwargs):

django/db/models/ in get_or_create(self, **kwargs)
    238             params.update(defaults)
    239             obj = self.model(**params)
--> 240   
    241             return obj, True

django/db/models/ in save(self)
    202                 cursor.execute("INSERT INTO %s (%s) VALUES (%s)" % \
    203                     (backend.quote_name(self._meta.db_table), ','.join(field_names),
--> 204                     ','.join(placeholders)), db_values)
    205             else:
    206                 # Create a new record with defaults for everything.

django/db/backends/ in execute(self, sql, params)
     10         start = time()
     11         try:
---> 12             return self.cursor.execute(sql, params)
     13         finally:
     14             stop = time()

django/db/backends/sqlite3/ in execute(self, query, params)
     90     def execute(self, query, params=()):
     91         query = self.convert_query(query, len(params))
---> 92         return Database.Cursor.execute(self, query, params)
     94     def executemany(self, query, param_list):

<class 'sqlite3.IntegrityError'>: testing_choice.poll_id may not be NULL

Attachments (1)

get_or_create.diff (3.7 KB) - added by Jan Rademaker <j.rademaker@…> 10 years ago.
Patch + tests

Download all attachments as: .zip

Change History (12)

comment:1 Changed 11 years ago by Antti Kaihola

The work-around is:

php, created = what.choice_set.get_or_create(poll=what, choice='PHP', votes=1)

But it obviously isn't DRY :)

comment:2 Changed 11 years ago by Brian Beck

This bug also affects generic relation managers (see #2316}).

I tried to debug this, but it's pretty elusive. I think the solution might be to define get_or_create in the subclass anywhere create is also defined in the subclass. For instance, GenericRelatedObjectManager and ManyRelatedManager (among others, perhaps) both define a create method, but no get_or_create method. get_or_create is not defined to actually call its own class's create method (in QuerySet for instance, it duplicates create's code).

comment:3 Changed 11 years ago by Antti Kaihola

Even worse, it seems that for many-to-many relations, the get_or_create method does create the related object but doesn't add a relation nor gives any error message.

For instance if you have model "Tag" with a field "name" and a model "BlogPost" with "tags=ManyToManyField(Tag)", then

myblogpost.tags.get_or_create(name='language_wars', defaults={'name':'language_wars'})

will create a Tag object with the correct name, but myblogpost.tags.all() is left unchanged.

In my opinion, the get_or_create method for both ForeignKeys and ManyToManyFields should be removed or throw a NotImplemented exception as long as it doesn't work correctly. The current functionality will confuse people.

Changed 10 years ago by Jan Rademaker <j.rademaker@…>

Attachment: get_or_create.diff added

Patch + tests

comment:4 Changed 10 years ago by Jan Rademaker <j.rademaker@…>

Has patch: set

Basically, I just copied the get_or_create method from (QuerySet.get_or_create).

comment:5 Changed 10 years ago by Jacob

Triage Stage: UnreviewedAccepted

comment:6 Changed 9 years ago by Christoph Neuroth <christoph.neuroth@…>

Cc: christoph.neuroth@… added

comment:7 Changed 9 years ago by Chris Beaven

Triage Stage: AcceptedReady for checkin

I've been using this patch for a while now. I can't see a reason why it's not ready for checkin.

comment:8 Changed 9 years ago by Malcolm Tredinnick

milestone: 1.0
Triage Stage: Ready for checkinAccepted

This doesn't have the same error checking as normal get_or_create() (if the save() fails). The patch needs more work and isn't ready for checkin yet. Also needs savepoint() additions to handle transactional support properly on PostgreSQL (again, as in the standard method).

The behaviour's inconsistent, so this is 1.0 if a proper patch can be produced.

comment:9 Changed 9 years ago by Gary Wilson

Owner: changed from nobody to Gary Wilson
Status: newassigned

comment:10 Changed 9 years ago by Gary Wilson

Resolution: fixed
Status: assignedclosed

(In [8415]) Fixed #3121 -- Made get_or_create() work for RelatedManager and ManyRelatedManager.

comment:11 Changed 6 years ago by Jacob

milestone: 1.0

Milestone 1.0 deleted

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