ForeignKey and *_set accessor method broke

[matthewharrison@…]

I revved to v3278 and my app broke. In my view I adjust some fields of the model.

My model looks something like this

class Foo(models.Model):
    name = models.CharField(maxlength=30)

class Bar(model.Model):
    foo = models.ForeignKey(Foo)
    data = models.CharField(maxlength=30)

later on I iterate over my bars and try and get my foos from them. ie

for foo in bar.foo_set.all():
    #do something with foo

I now get an attribute error when trying to do this:

AttributeError at /fooapp/
'Bar' object has no attribute 'foo_set'
Request Method: 	GET
Request URL: 	http://localhost:8000/fooapp/
Exception Type: 	AttributeError
Exception Value: 	'Bar' object has no attribute 'foo_set' 

Just wondering if there was a change that broke then _set functionality recently

I apologize for how vague this is. I have another model that has a foreign key and code similar to the above still works with that. I've briefly diffed the sources didn't chance on anything that looked to cause this change....

[anonymous]

OK, this is going to sound confusing, because you are overloading the "foo" and "bar" words way more than can be healthy, but here goes...

foo_set refers to the reverse side of the relation from Foo back to Bar. If you want to refer to the relation in a Bar object, just use bar.foo, it's a simple attribute. If you want to iterate over all the things that refer to a particular Foo -- call him fred -- then

for b in fred.foo_set.all():
   ...

All documented here: ​http://www.djangoproject.com/documentation/db_api/#backward

[Malcolm Tredinnick]

Stupid not logged in status. That was me in the last comment, for the record.

[James Bennett]

And just to clarify it conceptually, this goes back to foreign keys being a one-to-many relationship. To take an example from the official tutorial, you have Polls and Choices. A Choice only ever belongs to one Poll, so you access that as choice.poll. But a Poll has many Choices, so you access them via poll.choice_set.

[matt]

I'm sorry, I messed up my foos and bars. Let me try again. (Not using
foo nor bar). Yes, that example was wrong, but here's a simpler version of the code that is failing. (Yes I've read the tutorial)

I have a Component object, a Version object and a Data object (that
holds additional data about the version object). They look like
this::

class Component(models.Model):
   name = models.CharField(maxlenth=30)
   ...

class Version(models.Model):
   component = models.ForeignKey(Component)
   version = models.CharField(maxlength=30)
   ...

class Data(models.Model):
   meta_data = models.CharField(maxlength=30)
   version = models.ForeignKey(Version)

Now given a component, I want to get all the version instances and
alll the data associated with it. So I do something like this:

for version in component_instance.version_set.all():
   for data in version.data_set.all():
       #adjust meta_data on data

Here's the error

AttributeError at /myapp/
'Version' object has no attribute 'data_set'
Request Method:         GET
Request URL:    http://localhost:8000/myapp/
Exception Type:         AttributeError
Exception Value:        'Version' object has no attribute 'data_set'
Exception Location:     /home/matt/.views.py in _add_metadata, line 293

So this is the weird thing. Accessing _set.all() works on the
component_instance, but fails on the next line... Is _set.all() no
longer returning instances? Again, this worked before updating svn.

[matt]

I'm closing this since I appear to be a complete idiot. I guess I had a typo somewhere, which I somehow fixed and somehow now it's working...

Sorry for barking up the wrong tree...