# Django 4.0.8.dev20220803071047 - dokumentacja

# PostgreSQL specific query expressions

These expressions are available from the `django.contrib.postgres.expressions` module.

## `ArraySubquery()` expressions

class `ArraySubquery`(queryset)

New in Django 4.0.

`ArraySubquery` is a `Subquery` that uses the PostgreSQL `ARRAY` constructor to build a list of values from the queryset, which must use `QuerySet.values()` to return only a single column.

This class differs from `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}]