======================================
PostgreSQL specific database functions
======================================

All of these functions are available from the
``django.contrib.postgres.functions`` module.

.. currentmodule:: django.contrib.postgres.functions

``RandomUUID``
==============

.. class:: RandomUUID()

Returns a version 4 UUID.

The `pgcrypto extension`_ must be installed. You can use the
:class:`~django.contrib.postgres.operations.CryptoExtension` migration
operation to install it.

.. _pgcrypto extension: https://www.postgresql.org/docs/current/static/pgcrypto.html

Usage example::

    >>> from django.contrib.postgres.functions import RandomUUID
    >>> Article.objects.update(uuid=RandomUUID())

``TransactionNow``
==================

.. class:: TransactionNow()

Returns the date and time on the database server that the current transaction
started. If you are not in a transaction it will return the date and time of
the current statement. This is a complement to
:class:`django.db.models.functions.Now`, which returns the date and time of the
current statement.

Note that only the outermost call to :func:`~django.db.transaction.atomic()`
sets up a transaction and thus sets the time that ``TransactionNow()`` will
return; nested calls create savepoints which do not affect the transaction
time.

Usage example::

    >>> from django.contrib.postgres.functions import TransactionNow
    >>> Article.objects.filter(published__lte=TransactionNow())
    <QuerySet [<Article: How to Django>]>
