Django: get unique object list from QuerySet

问题:

I have the following (simplified) models in my Django app:

class Color(models.Model):
    name = models.CharField(max_length=10)

class Item(models.Model):
    name = models.CharField(max_length=200)
    color = models.ForeignKey(Color, blank=True, null=True)

class Favorite(models.Model):
    user = models.ForeignKey(User)
    item = models.ForeignKey(Item)

I'm currently getting all the items I need using the following query:

favorites = Favorite.objects.filter(user=request.user)

How can I get all the distinct colors for the items in that QuerySet?

I need the a list of the actual color objects, not just the color ids, which I can get using

favorites.values_list('item__color').distinct

回答1:

If I understand you correctly, the following should do the trick:

favorites = Favorite.objects.filter(user=request.user)
color_ids = favorites.values_list('item__color', flat=True).distinct()
colors = Color.objects.filter(id__in=color_ids)

There has to be a cleaner way than that though.

Edit: A much cleaner solution:

colors = Color.objects.filter(item__favorite__user=request.user).distinct()

回答2:

Can you do:

Color.objects.filter(item__favorite__user = request.user).distinct()

You might have to set some related_names on your foreign keys if these aren't the defaults (I can never remember the defaults).

回答3:

Can you do:

favorites = Favorite.objects.filter(user=request.user).distinct('item__color')

回答4:

The is values_list(*fields, flat=False, named=False) method, so run it on your objects, for example:

user.groups.values_list('name', flat=True)