How do I query objects of a ManyToManyField?(without through)

Question

The given below are the models for a retail store.

class Rack(models.Model):
    name = models.CharField(max_length=128)
    number = models.PositiveSmallIntegerField()
    categories = models.ManyToManyField(Category)


class Category(models.Model):
    name = models.CharField(max_length=128)
    code = models.CharField(max_length=3)


class Product(models.Model):
    title = models.CharField(max_length=255)
    in_stock = models.BooleanField(default=False)
    categories = models.ManyToManyField(Category)

Rack : the rack where the products are stocked. Category : the Category of the product. Product : the product

A rack can have multiple categories and same category can be on multiple racks. for ease of managing, I prefer selecting categories on a rack at admin, so prefered this design.

If given a rack, say No.1, How do I query the products on the given rack?

>> Rack.objects.get(number=1).categories.all()

[<Category: Fruits>, <Category: Vegetables>]

I don't want to iterate this query set, but to make a query to return the objects.

my question is, How do I query the objects on a rack as optimized as possible?

so that the query must return a list of objects.

>> Rack.objects.filter( * code here to get the objects in the rack 1 * ) must returns the objects on the rack 1
[<Product: Apple>, <Product: Orange>, <Product: Cucumber>, <Product: Carrot>, <Product: Green Chillie>, <Product: Onion>, <Product: Grapes> ]

Thanks

duplicate: http://stackoverflow.com/questions/4881783/django-reverse-lookups-with-manytomanyfield — Aaron Lelevier, Nov 05 '15 at 00:46
@AronYsidoro Don't worry, this is not a duplicate, both the questions are on `ManyToManyField` while mine have nothing to do with `through`. — All Іѕ Vаиітy, Nov 05 '15 at 10:41

Mike Covington · Answer 1 · 2015-11-05T18:21:26.233

1

Your best bet might be to use a through model. If you don't want to do that, I'd try out something like this:

categories = Rack.objects.get(number=1).categories.all().values_list('name', flat=True)
Product.objects.filter(categories__name__in=categories)

Also, do you mean for this:

class Product(models.Model):
    ...
    Category = models.ManyToManyField(Category)

to be:

class Product(models.Model):
    ...
    categories = models.ManyToManyField(Category)

like in your Rack model?

edited Nov 05 '15 at 18:21

answered Nov 05 '15 at 01:32

Mike Covington

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yeah it is `categories`, can this be done with a single query than with two? – All Іѕ Vаиітy Nov 05 '15 at 10:44
Thank you for this answer. will accept if not found a more optimized answer. – All Іѕ Vаиітy Nov 05 '15 at 18:20

How do I query objects of a ManyToManyField?(without through)

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