mirror of
https://github.com/django/django.git
synced 2024-12-24 10:05:46 +00:00
38 lines
1.4 KiB
Plaintext
38 lines
1.4 KiB
Plaintext
=====================================
|
|
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}]
|