Is there a way to query reverse in django models?

Question

I know this question has been answered in different ways but i'm still unable to see the clear picture. I have the following tables with following relationships:

class Category(models.Model):
name = models.CharField(max_length=100, null=False, blank=False)

def __str__(self):
    return self.name


class SubCategory(models.Model):
    sub_name = models.CharField(max_length=100, null=False, blank=True, default='None')
    category = models.ManyToManyField(Category, default=1)

class Product(models.Model):

    name = models.CharField(max_length=150, null=False, blank=False)
    brand = models.CharField(max_length=100, null=False, blank=False)
    price = models.FloatField(null=False, blank=False)
    weight = models.CharField(max_length=100,null=False, blank=False)

    sub_category = models.ForeignKey(SubCategory, on_delete=models.SET_DEFAULT, default=13)
    category = models.ForeignKey(Category, on_delete= models.CASCADE)

I am trying to solve two queries as follows:

Fetch all the category and subcategories to a specific category where the brand is given. Display structure that i'm making is Brand(Men->Shirts,Pants etc. Women->Shirts,Pants etc).

NOTE: Each brand can sell products of multiple categories and subcategories.

Fetch all the subcategories where the category name must be taken out from the result of Category.objects.all(). Display structure that i'm making here is Men(its sub categories) , Women(its sub categories)

vestronge vestronge · Accepted Answer · 2020-07-21T23:11:57

Let us take it step by step

Get all products for a specific brand

Product.objects.filter(brand=brand)

Now we want to list down the categories for this match. We'll get the ids of categories instead

Product.objects.filter(brand=brand).values_list("category_id", flat=True)

Now let us get the corresponding category objects

queryset = Product.objects.filter(brand=brand).values_list("category_id", flat=True)
categories = Category.objects.filter(id__in=queryset)

Note: If you just want to fetch the category names, you can do

Product.objects.filter(brand=brand).values_list("category__name", flat=True).distinct()

Is there a way to query reverse in django models?

1 Answers