Fixed #11964 -- Added support for database check constraints.

docs/ref/models/check-constraints.txt

@@ -0,0 +1,46 @@
+===========================
+Check constraints reference
+===========================
+
+.. module:: django.db.models.constraints
+
+.. currentmodule:: django.db.models
+
+.. versionadded:: 2.2
+
+The ``CheckConstraint`` class creates database check constraints. They are
+added in the model :attr:`Meta.constraints
+<django.db.models.Options.constraints>` option. This document
+explains the API references of :class:`CheckConstraint`.
+
+.. admonition:: Referencing built-in constraints
+
+    Constraints are defined in ``django.db.models.constraints``, but for
+    convenience they're imported into :mod:`django.db.models`. The standard
+    convention is to use ``from django.db import models`` and refer to the
+    constraints as ``models.CheckConstraint``.
+
+``CheckConstraint`` options
+===========================
+
+.. class:: CheckConstraint(constraint, name)
+
+    Creates a check constraint in the database.
+
+``constraint``
+--------------
+
+.. attribute:: CheckConstraint.constraint
+
+A :class:`Q` object that specifies the condition you want the constraint to
+enforce.
+
+For example ``CheckConstraint(Q(age__gte=18), 'age_gte_18')`` ensures the age
+field is never less than 18.
+
+``name``
+--------
+
+.. attribute:: CheckConstraint.name
+
+The name of the constraint.

docs/ref/models/index.txt

@@ -9,6 +9,7 @@ Model API reference. For introductory material, see :doc:`/topics/db/models`.
 
    fields
    indexes
+   check-constraints
    meta
    relations
    class

docs/ref/models/options.txt

@@ -451,6 +451,26 @@ Django quotes column and table names behind the scenes.
 
         index_together = ["pub_date", "deadline"]
 
+``constraints``
+---------------
+
+.. attribute:: Options.constraints
+
+    .. versionadded:: 2.2
+
+    A list of :doc:`constraints </ref/models/check-constraints>` that you want
+    to define on the model::
+
+        from django.db import models
+
+        class Customer(models.Model):
+            age = models.IntegerField()
+
+            class Meta:
+                constraints = [
+                    models.CheckConstraint(models.Q(age__gte=18), 'age_gte_18'),
+                ]
+
 ``verbose_name``
 ----------------