如何获取 ManyToMany 字段中的值的计数

Question

I have a model called Recipe that is simplified to have a title and category. The category is a ManyToMany field.

class Recipe(models.Model):
    title = models.CharField(max_length=100)
    category = models.ManyToManyField(Category, help_text='Select a category')

I have another model called Category

class Category(models.Model):
    name = models.CharField(max_length=200, help_text='Enter a baking category')

    def __str__(self):
        return self.name

There are several categories but for simplicity, let's say we have two: Bread and Cake. How would I query the DB to figure out how many Recipes I have of each category?

I've been trying something like this:

total_bread= Recipe.objects.filter(categories=1).annotate(category_count=Count('Bread'))

But that isn't working. I also don't want to explicitly define all the categories I'm looking for since in the future I would add more categories.

Answer 1

Since you want the count of how many recipes there are for each Category you should annotate on it instead of on Recipe :

categories = Category.objects.annotate(recipe_count=Count('recipe'))

for category in categories:
    print(category.name, category.recipe_count)

# For particular category:
bread = Category.objects.annotate(recipe_count=Count('recipe')).get(name='Bread')
print(bread.recipe_count)