From 3aa545281e0c0f9fac93753e3769df9e0334dbaa Mon Sep 17 00:00:00 2001
From: Hannes Ljungberg <hannes.ljungberg@gmail.com>
Date: Sat, 6 Feb 2021 20:45:54 +0100
Subject: Fixed #30916 -- Added support for functional unique constraints.

Thanks Ian Foote and Mariusz Felisiak for reviews.
---
 docs/ref/checks.txt                   |  2 ++
 docs/ref/contrib/postgres/indexes.txt | 22 ++++++++++++++++++----
 docs/ref/models/constraints.txt       | 22 +++++++++++++++++++++-
 3 files changed, 41 insertions(+), 5 deletions(-)

(limited to 'docs/ref')

diff --git a/docs/ref/checks.txt b/docs/ref/checks.txt
index 7761a2a323..dbba801e39 100644
--- a/docs/ref/checks.txt
+++ b/docs/ref/checks.txt
@@ -391,6 +391,8 @@ Models
 * **models.W042**: Auto-created primary key used when not defining a primary
   key type, by default ``django.db.models.AutoField``.
 * **models.W043**: ``<database>`` does not support indexes on expressions.
+* **models.W044**: ``<database>`` does not support unique constraints on
+  expressions.
 
 Security
 --------
diff --git a/docs/ref/contrib/postgres/indexes.txt b/docs/ref/contrib/postgres/indexes.txt
index b6a4aba808..9a9b7fc73b 100644
--- a/docs/ref/contrib/postgres/indexes.txt
+++ b/docs/ref/contrib/postgres/indexes.txt
@@ -183,10 +183,10 @@ available from the ``django.contrib.postgres.indexes`` module.
 .. class:: OpClass(expression, name)
 
     An ``OpClass()`` expression represents the ``expression`` with a custom
-    `operator class`_ that can be used to define functional indexes. To use it,
-    you need to add ``'django.contrib.postgres'`` in your
-    :setting:`INSTALLED_APPS`. Set the ``name`` parameter to the name of the
-    `operator class`_.
+    `operator class`_ that can be used to define functional indexes or unique
+    constraints. To use it, you need to add ``'django.contrib.postgres'`` in
+    your :setting:`INSTALLED_APPS`. Set the ``name`` parameter to the name of
+    the `operator class`_.
 
     For example::
 
@@ -197,4 +197,18 @@ available from the ``django.contrib.postgres.indexes`` module.
 
     creates an index on ``Lower('username')`` using ``varchar_pattern_ops``.
 
+    Another example::
+
+        UniqueConstraint(
+            OpClass(Upper('description'), name='text_pattern_ops'),
+            name='upper_description_unique',
+        )
+
+    creates a unique constraint on ``Upper('description')`` using
+    ``text_pattern_ops``.
+
+    .. versionchanged:: 4.0
+
+        Support for functional unique constraints was added.
+
     .. _operator class: https://www.postgresql.org/docs/current/indexes-opclass.html
diff --git a/docs/ref/models/constraints.txt b/docs/ref/models/constraints.txt
index e3b682d1c5..c675903db6 100644
--- a/docs/ref/models/constraints.txt
+++ b/docs/ref/models/constraints.txt
@@ -69,10 +69,30 @@ constraint.
 ``UniqueConstraint``
 ====================
 
-.. class:: UniqueConstraint(*, fields, name, condition=None, deferrable=None, include=None, opclasses=())
+.. class:: UniqueConstraint(*expressions, fields=(), name=None, condition=None, deferrable=None, include=None, opclasses=())
 
     Creates a unique constraint in the database.
 
+``expressions``
+---------------
+
+.. attribute:: UniqueConstraint.expressions
+
+.. versionadded:: 4.0
+
+Positional argument ``*expressions`` allows creating functional unique
+constraints on expressions and database functions.
+
+For example::
+
+    UniqueConstraint(Lower('name').desc(), 'category', name='unique_lower_name_category')
+
+creates a unique constraint on the lowercased value of the ``name`` field in
+descending order and the ``category`` field in the default ascending order.
+
+Functional unique constraints have the same database restrictions as
+:attr:`Index.expressions`.
+
 ``fields``
 ----------
 
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