CODEWITHSUNDEEP
django
user1328021
user1328021

Reputation: 9840

Getting all unique values stored in a many-to-many field

I have a many-to-many field called categories and I would like to get distinct values stored in that field.

The following is my model:

class Book (models.Model):
    categories=models.ManyToManyField(Category, related_name = 'categories', blank = True, null=True)

Here is my Category model:

class Category (MPTTModel):
    category = models.CharField(max_length=250)
    parent = TreeForeignKey('self', blank=True, null=True, related_name='children')

I'd like to get every single one of the categories related to a book. How would I do this?

Upvotes: 3

Views: 4652

Answers (2)

Rohan
Rohan

Reputation: 53336

If you want to get categories related to one instance of book, do book_inst.category_set.all(). There will not be duplicates.

But I think, you want to get all Categories which are related to any Book, you can do:

Category.objects.filter(categories__in=[Book.objects.all()]).distinct()

Upvotes: 6

Raunak Agarwal
Raunak Agarwal

Reputation: 7228

Basically, you need a reverse lookup from the category side to check if there is book for that category if yes, add to the resultant query set. Since, the related_name argument in the Book is 'categories', your reverse lookup would look something like this.

  Category.objects.filter(categories__in = Book.objects.all())

Upvotes: 0

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