subquery must return only one column

[Mohammad Ali Mehdizadeh]

I have two tables:

class Product(models.Model):
    name = models.CharField(max_length=127)
    category = models.ForeignKey('Category', on_delete=models.CASCADE, related_name='products')


class Category(models.Model):
    name = models.CharField(max_length=127)
    parent = models.ForeignKey('self', on_delete=models.CASCADE, null=True, blank=True, related_name='children')

I want to get all categories that have at least one product-related or their children to have at least one product.
So I have a query like:

Category.objects.all().annotate(product_count_parent=Count('products')).filter(Q(product_count_parent__gt=0) | Q(children__id__in=Category.objects.filter(children=None).annotate(product_count=Count('products')).filter(product_count__gt=0)))

I have gotten this error

ProgrammingError: subquery must return only one column
LINE 1: ... GROUP BY "nakhll_market_category"."id", T3."id", (SELECT U0...

[Simon Charette]

You are using an __in=QuerySet filter ​without limiting the columns returned by your inner query.

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