DatabaseError while saving with force_update set

[fva]

Models:

class A ( models.Model ) :
    a = models.IntegerField ( null=True )

class B ( A ) : pass

session:

In [3]: b = B()

In [4]: b.save()

In [5]: b.save ( force_update = True )
---------------------------------------------------------------------------
DatabaseError                             Traceback (most recent call last)

<ipython console> in <module>()

django/db/models/base.pyc in save(self, force_insert, force_update, using)
    428         if force_insert and force_update:
    429             raise ValueError("Cannot force both insert and updating in model saving.")
--> 430         self.save_base(using=using, force_insert=force_insert, force_update=force_update)
    431 
    432     save.alters_data = True

django/db/models/base.pyc in save_base(self, raw, cls, origin, force_insert, force_update, using)
    496                         rows = manager.using(using).filter(pk=pk_val)._update(values)
    497                         if force_update and not rows:
--> 498                             raise DatabaseError("Forced update did not affect any rows.")
    499                 else:
    500                     record_exists = False

DatabaseError: Forced update did not affect any rows.

but simple b.save() updates fine.

[Alex Gaynor]

That behavior looks correct. An unsaved model (one with no pk) can't be updated. Pretty much don't use the force_insert/force_update if you don't have a good reason.

[Karen Tracey]

The model was saved, in step 4. It does have a PK:

>>> from ttt.models import B
>>> b = B()
>>> b.pk
>>> b.a
>>> b.save()
>>> b.pk
2
>>> b.a
>>> b.save(force_update=True)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "C:\u\kmt\django\trunk\django\db\models\base.py", line 435, in save
    self.save_base(using=using, force_insert=force_insert, force_update=force_update)
  File "C:\u\kmt\django\trunk\django\db\models\base.py", line 503, in save_base
    raise DatabaseError("Forced update did not affect any rows.")
DatabaseError: Forced update did not affect any rows.
>>>

[Alex Gaynor]

Doh, my apologies.

[Gregor Müllegger]

First tests that fail for the inherited model that is no proxy and has no custom fields specified.

[Gregor Müllegger]

The problem is that the subclass has no custom fields assigned. So the subclassed model will try to make an update query without and values this results in an empty query.

There is a very simple fix for this, added in the second patch. This avoids making the empty query that ofcourse doesn't affect any rows which causes the error.

Maybe someone with a better understanding of the ORM could have a look if this fix is sufficient and confirm that it doesn't have sideeffects to NOT execute the update query if there is nothing to change.

[Gregor Müllegger]

Patch with tests and a possible, simple fix.

[patchhammer]

13864.tests_and_possible_fix.patch fails to apply cleanly on to trunk

[Ramiro Morales]

Patch updated to r16288.

[markb1]

Patch updated to r17083. All relevant tests pass.

[Karen Tracey]

In [17088]:

Fix #13864: Removed database error raised when force_update is requsted on save of an inherited model with no fields of its own. Thanks fva, gregmuellegger, and markb1.