Django ManyToManyField filter with parameters?

Question

I have such models:

class Category(Model):
    ...
    type = models.CharField(max_length=255, choices=settings.CATEGORIES)

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

I have the list of categories, entered by user (format is arbitrary):

c = [<Category: G, type: producer>, <Category: L, type: producer>, <Category: Teen, type: age>, <Category: Man, type: sex>]

Now I want to have all products that in categories have 'G' or 'L' with type 'producer', 'Teen' with type 'age' and 'Man' with type 'sex'. I'm doing for example next queryset:

Product.objects.filter(Q(categories=c[0])|Q(categories=c[1]), Q(categories=c[2]), Q(categories=c[3])

that have such query:

SELECT "shop_product"."id", "shop_product"."title", "shop_product"."description",
"shop_product"."price", "shop_product"."code", "shop_product"."stored_count",
"shop_product"."sold_count", "shop_product"."added_date" FROM "shop_product"
INNER JOIN     "shop_product_categories" ON ("shop_product"."id" =   
"shop_product_categories"."product_id")    WHERE 
(("shop_product_categories"."category_id" = 1 OR 
"shop_product_categories"."category_id" = 2) AND    
"shop_product_categories"."category_id" = 4 AND 
"shop_product_categories"."category_id" = 6)

I have at least one objects, that suits such requirements, but queryset returns nothing. Any suggests?

Answer 1

You need to do cascading filtering, otherwise the current select will return all products that have "shop_product_categories"."category_id" with value of 1/2 and 4 and 6 at the same time... Here is an example queryset that will return what you want:

Product.objects.filter(categories__in=c[0:2])
               .filter(categories=c[2])
               .filter(categories=c[3])
               .distinct()

Which generates SQL like this:

SELECT DISTINCT "test1_product"."id" FROM "test1_product" INNER JOIN "test1_product_categories" ON ("test1_product"."id" = "test1_product_categories"."product_id") 
    INNER JOIN "test1_product_categories" T4 
        ON ("test1_product"."id" = T4."product_id")
    INNER JOIN "test1_product_categories" T6 
        ON ("test1_product"."id" = T6."product_id") 
WHERE ("test1_product_categories"."category_id" IN (1, 2) 
    AND T4."category_id" = 3 
    AND T6."category_id" = 4 )