Question

My question is similar to this, but creating junction table is not good in this particular case.

Short snippet of a model:

class Item(models.Model):
    photos = models.ManyToManyField('Photo', blank=True, null=True, related_name='photo_in_%(class)ss')

    class Meta:
        abstract = True 

Then I have many classes like this:

class Article(Item): pass
class BlogEntry(Item): pass
class Country(Item): pass
...

And of course:

class Photo(models.Model):
    pass

Having e.g. a = Article() I can easily get photos in article with a.photos.all()

The question is: having p = Photo() how to retrieve all objects with this photo?

But:

Generic relation is not an option. Each photo can be in various items’ photos simultaneously.

I came up with such a method, though. But it uses eval and eval is evil…

class Photo(models.Model):
    def get_items_with_photo(self):
        items = []
        for cl in [name for name in dir(self) if name.startswith('photo_in')]:
            qset = eval('self.%s.all()' % (cl))
            [items.append(item) for item in qset]
        return items

I would appreciate any different (better) solution.

Answer 1

Instead of:

qset = eval('self.%s.all()' % (cl))

do:

photo_attr = getattr(self, cl)
qset = photo_attr.all()