Opened 8 years ago

Closed 8 years ago

Last modified 8 years ago

#9553 closed (invalid)

Save of ForeignKeys's model doesn't cause update of _id field

Reported by: Oldřich Jedlička Owned by: nobody
Component: Database layer (models, ORM) Version: 1.0
Severity: Keywords:
Cc: Triage Stage: Unreviewed
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: UI/UX:


For two models

class Inner(models.Model):
    field = models.CharField(max_length=10)

class Outer(models.Model):
    inner = models.ForeignKey(Inner)
    other_field = models.CharField(max_length=15)

It is not possible to write

inner = Inner(field="test")
outer = Outer(inner=inner, other_field="other test")

It ends-up with

IntegrityError: null value in column "inner_id" violates not-null constraint

Attachments (1)

django-related_model_fix.patch (1.9 KB) - added by Oldřich Jedlička 8 years ago.
Proof of concept plus test

Download all attachments as: .zip

Change History (8)

comment:1 Changed 8 years ago by Karen Tracey

Needs documentation: unset
Needs tests: unset
Patch needs improvement: unset
Resolution: invalid
Status: newclosed

Right, inner does not have a primary key value until you call save() on it. So you cannot correctly specify it as the target of outer's key before then. Your code should be:

inner = Inner(field="test")
outer = Outer(inner=inner, other_field="other test")

I'm pretty sure this is spelled out somewhere in the docs though I can't find it at the moment. The fact that save() is what creates the object's pk is noted here:

comment:2 Changed 8 years ago by Oldřich Jedlička

Resolution: invalid
Status: closedreopened

Actually the problem is not that the itself doesn't update the outer's inner_id field, the problem is that the inner_id field is not "intelligently" taken from inner's pk during Outer has all the information to be able to save itself.

To illustrate the problem in detail here is a working code snippet:
outer.inner = outer.inner

My opinion is that this is not the "right thing". If you think this is really wanted behaviour, feel free to close the ticket.

This is from my real-life project (not with Inner and Outer classes, of course). I can live with the workaround, but this doesn't follow the DRY principle.

comment:3 Changed 8 years ago by Oldřich Jedlička

The root cause of the problem is that there are two fields for the same thing:

  • inner_id (Inner's primary key as part of model)
  • inner (Inner instance)

comment:4 Changed 8 years ago by Oldřich Jedlička

Has patch: set

With the attached patch the saving works like a charm. I got inspired by the parent's pk update machinery in Model.save_base and used it to update all RelatedField's pk (that is maybe wrong).

comment:5 Changed 8 years ago by Alex Gaynor

I'm not entirely sure I follow the issue, but either way, can you please include a test in your patch that fails before your patch is applied, and passes afterwords.

Changed 8 years ago by Oldřich Jedlička

Proof of concept plus test

comment:6 Changed 8 years ago by James Bennett

Resolution: invalid
Status: reopenedclosed

This is, I believe, intended behavior: assigning an object to a relation before it has a value for whatever column is used in the relation isn't supposed to work. If you wish to argue for that as a new feature in Django, please take it to the django-developers mailing list rather than endlessly reopening this ticket.

comment:7 Changed 8 years ago by Oldřich Jedlička

All my arguments are here (the model has all the information for save), so let's leave it closed. I do not want to argue for such a stupid thing :-)

Note: See TracTickets for help on using tickets.
Back to Top