Fixed #30916 -- Added support for functional unique constraints.

Thanks Ian Foote and Mariusz Felisiak for reviews.

1 files changed, 21 insertions, 1 deletions

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``
 ----------