Tag "subquery"

PostgreSQL JSON subqueries

#### Allows to fetch a row or array of rows of data, linked to parent object, in a single query. Data is fetched as JSON and is not serialized into Django objects. ##### Example: from django.db import Models class Book(models.Model): authors = models.ManyToMany('Author', through='BookToAuthor', blank=True) title = models.CharField(max_length=512, default='') class Author(models.Model): name = models.CharField(max_length=512, default='') class BookToAuthor(models.Model): author = models.ForeignKey(Author, on_delete=models.CASCADE) book = models.ForeignKey(Book, on_delete=models.CASCADE) ##### Download author with all his/her books in a single query from django.db.models import OuterRef books_by_author_subquery = Book.objects.filter( id__in=BookToAuthor.objects.filter(author_id=OuterRef(OuterRef('id'))) ).values('title') author = Author.objects\ .annotate(books=SubqueryJsonAgg(books_by_author_subquery))\ .get(id=1)