Fixed #32776 -- Added support for Array subqueries on PostgreSQL.

docs/ref/contrib/postgres/expressions.txt

@@ -0,0 +1,37 @@
+=====================================
+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)
+
+.. versionadded:: 4.0
+
+``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::
+
+    >>> 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}]

docs/ref/contrib/postgres/index.txt

@@ -30,6 +30,7 @@ a number of PostgreSQL specific data types.
 
     aggregates
     constraints
+    expressions
     fields
     forms
     functions