Retrieve All Records Which Only Have Children Records

Question

If I have the following two models:

class Blog(models.Model):
    title = models.CharField(max_length=160)
    text = models.TextField()

class Comment(models.Model):
    blog = models.ForeignKey(Blog)
    text = models.TextField()

As you can see, a Blog may have many Comments, but a Comment may only have one Blog.

How can I get all of the Blogs which only have Comments?

Thanks How

Answer 1

You can use Blog.objects.filter(comment__isnull=False) this will return all blog instances has comment relation. You can also check comment__text__isnull=False or anything you need to filter about comments. The SQL equivalent of the query above is: SELECT "app_blog"."id", "app_blog"."title", "app_blog"."text" FROM "app_blog" INNER JOIN "app_comment" ON ("app_blog"."id" = "app_comment"."blog_id") WHERE "app_comment"."id" IS NOT NULL where app prefix is the name of django app