> I have a generic relation Flag, with a FlagType:
>
> class FlagType(models.Model):
> name = models.CharField(maxlength=50)
> description = models.TextField()
>
> class Flag(models.Model):
> type = models.ForeignKey(FlagType) # type of flag
> content_type = models.ForeignKey(ContentType)
> object_id = models.PositiveIntegerField()
> content_object = generic.GenericForeignKey()
> user = models.ForeignKey(User)
> created = models.DateTimeField()
>
> So, for example "illegal" or "to feature" would be flags. Now we're
> flagging Song objects and I would like a queryset that gets me all Songs
> flagged with a flag of type "illegal".
>
> I can do:
>
> flag = FlagType.objects.get(name='illegal')
> ctype = ContentType.objects.get_for_model(Song)
> flagged = Flag.objects.filter(type=flag,
> content_type=ctype).order_by('-created')
> songs = [item.content_object for item in flagged ]
>
> But the problem is: I can't do extra things to this list like order_by()
> or an extra filter() or exclude().
>
> How can I get the same result, but still have a queryset (containing
> Songs) instead of a list??
This looks similar to what the TaggedItemManager needs to do in
django-tagging [1] - here's a completely untested, adapted version of
its get_by_model method - does this work for you?
models.py::
from django.contrib.contenttypes.models import ContentType
from django.db import backend, models
class FlagManager(models.Manager):
def get_by_model_and_flag_type(self, Model, type_name):
"""
Create a ``QuerySet`` containing instances of the given model
class associated with a ``FlagType`` with the given name.
"""
flag_type = FlagType.objects.get(name=type_name)
ctype = ContentType.objects.get_for_model(Model)
rel_table = backend.quote_name(self.model._meta.db_table)
return Model._default_manager.extra(
tables=[self.model._meta.db_table], # Use a non-explicit join
where=[
'%s.content_type_id = %%s' % rel_table,
'%s.type_id = %%s' % rel_table,
'%s.%s = %s.object_id' %
(backend.quote_name(Model._meta.db_table),
backend.quote_name(Model._meta.pk.column),
rel_table)
],
params=[ctype.id, flag_type.id],
)
class Flag(models.Model):
...
objects = FlagManager()
Usage::
songs = Flag.objects.get_by_model_and_flag_type(Song, 'illegal')
Regards,
Jonathan.
[1] http://code.google.com/p/django-tagging/
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