QuerySet .dates() method should span relationships

[coleifer]

In the current implementation, QuerySet.dates() cannot span relationships. This limits the date-based generic views to only working if the date_field is on the same model as your queryset. The actual object lookup for the date-based generic views *works* - it is when the generic view tries to build the date_list that it fails.

# here's a silly example of what I'm talking about
>>> from django.contrib.auth.models import Group, User
>>> User.objects.dates('last_login', 'year')
[datetime.datetime(2009, 1, 1, 0, 0), datetime.datetime(2010, 1, 1, 0, 0)]

>>> Group.objects.dates('user__last_login', 'year')
FieldDoesNotExist: Group has no field named 'user__last_login'

The error is raised by this call:
​http://code.djangoproject.com/browser/django/trunk/django/db/models/query.py#L991

I suspect this could be tweaked by changing something around here:
​http://code.djangoproject.com/browser/django/trunk/django/db/models/sql/subqueries.py#L187

[Valentin Golev]

tests

[Valentin Golev]

I hope I'm doing everything right

[Valentin Golev]

I don't think it really needs any changes in documentation. Patch is ready.

I had to move the verification logic to the django.models.sql.subqueries.DateQuery, I'm not really sure if it was the right thing to do (but I have no better ideas and I see no harm here).

[Valentin Golev]

patch

[anonymous]

Unfortunately this patch doesn't work for Multi-Table Inheritance models, i.e. ones which have an implicit one-to-one link to a parent model.

eg:

class Post():
    date_posted = models.DateTimeField()

class BlogPost(Post):
    pass

>> BlogPost.objects.dates('date_posted', 'year')
(1054, "Unknown column 'myapp_blogpost.date_posted' in 'where clause'")

or trying a 'wrong' trick...

>> BlogPost.objects.dates('post__date_posted', 'year')
(1054, "Unknown column 'myapp_blogpost.post' in 'where clause'")

It seems like there should be some helper

[anonymous]

"It seems like there should be some helper" ...I didn't finish that phrase.

What I meant to say is I have been trawling through the Django db classes to try and find... there must be some helper method somewhere which resolves the field names the 'right' way without having to write our own hack code to do so.

But so far I can't find it. I figure this ought to be easy for whoever wrote the relevant part of the ORM.

There's this bit of code on compiler.py > SQLCompiler.pre_sql_setup() that looks promising:

        if (not self.query.select and self.query.default_cols and not
                self.query.included_inherited_models):
            self.query.setup_inherited_models()

This will never happen for a DateQuery because of this, in subqueries.py > DateQuery.add_date_select():

    self.select = [select]

Unfortunately I don't know what most of this code really does, there's a bit too much going on to take it all in easily.

[anonymous]

Sorry everybody, please ignore everything I just said above. It looked like I'd definitely ran into this bug, but in fact I was causing the problem with a bit of bad raw sql in my custom model manager.

The implicit one-to-one field on Multi-Table Inheritance models seems to work just fine for queryset.dates().

Sorry again for the noise.

[Valentin Golev]

Anyway, I think we should add some tests for multi-table inheritance. I'll try to do it soon

[va1en0k]

I hope I'm not wrong

[Alex Gaynor]

(In [14461]) Fixed #13935, added support for using QuerySet.dates across related fields. Thanks to valyagolev for his work on the patch.