Add check constraint support - needed a few Field changes

2 files changed, 29 insertions, 3 deletions

diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 58ae3413f3..a0b09c9fec 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -232,12 +232,32 @@ class Field(object):
         # mapped to one of the built-in Django field types. In this case, you
         # can implement db_type() instead of get_internal_type() to specify
         # exactly which wacky database column type you want to use.
+        params = self.db_parameters(connection)
+        if params['type']:
+            if params['check']:
+                return "%s CHECK (%s)" % (params['type'], params['check'])
+            else:
+                return params['type']
+        return None
+
+    def db_parameters(self, connection):
+        """
+        Replacement for db_type, providing a range of different return
+        values (type, checks)
+        """
         data = DictWrapper(self.__dict__, connection.ops.quote_name, "qn_")
         try:
-            return (connection.creation.data_types[self.get_internal_type()]
-                    % data)
+            type_string = connection.creation.data_types[self.get_internal_type()] % data
         except KeyError:
-            return None
+            type_string = None
+        try:
+            check_string = connection.creation.data_type_check_constraints[self.get_internal_type()] % data
+        except KeyError:
+            check_string = None
+        return {
+            "type": type_string,
+            "check": check_string,
+        }
 
     @property
     def unique(self):
diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index 08cc0a747f..37bf4e8072 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -1050,6 +1050,9 @@ class ForeignKey(RelatedField, Field):
             return IntegerField().db_type(connection=connection)
         return rel_field.db_type(connection=connection)
 
+    def db_parameters(self, connection):
+        return {"type": self.db_type(connection), "check": []}
+
 class OneToOneField(ForeignKey):
     """
     A OneToOneField is essentially the same as a ForeignKey, with the exception
@@ -1292,3 +1295,6 @@ class ManyToManyField(RelatedField, Field):
         # A ManyToManyField is not represented by a single column,
         # so return None.
         return None
+
+    def db_parameters(self, connection):
+        return {"type": None, "check": None}