===================================== PostgreSQL specific query expressions ===================================== .. module:: django.contrib.postgres.expressions :synopsis: PostgreSQL specific query expressions These expressions are available from the ``django.contrib.postgres.expressions`` module. ``ArraySubquery()`` expressions =============================== .. class:: ArraySubquery(queryset) ``ArraySubquery`` is a :class:`~django.db.models.Subquery` that uses the PostgreSQL ``ARRAY`` constructor to build a list of values from the queryset, which must use :meth:`.QuerySet.values` to return only a single column. This class differs from :class:`~django.contrib.postgres.aggregates.ArrayAgg` in the way that it does not act as an aggregate function and does not require an SQL ``GROUP BY`` clause to build the list of values. For example, if you want to annotate all related books to an author as JSON objects: .. code-block:: pycon >>> from django.db.models import OuterRef >>> from django.db.models.functions import JSONObject >>> from django.contrib.postgres.expressions import ArraySubquery >>> books = Book.objects.filter(author=OuterRef("pk")).values( ... json=JSONObject(title="title", pages="pages") ... ) >>> author = Author.objects.annotate(books=ArraySubquery(books)).first() >>> author.books [{'title': 'Solaris', 'pages': 204}, {'title': 'The Cyberiad', 'pages': 295}]