1 files changed, 48 insertions, 0 deletions
diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index 1447787ce..4f58f6141 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -3202,6 +3202,52 @@ class _truncated_label(quoted_name):
         return self
 
 
+class conv(_truncated_label):
+    """Mark a string indicating that a name has already been converted
+    by a naming convention.
+
+    This is a string subclass that indicates a name that should not be
+    subject to any further naming conventions.
+
+    E.g. when we create a :class:`.Constraint` using a naming convention
+    as follows::
+
+        m = MetaData(naming_convention={
+            "ck": "ck_%(table_name)s_%(constraint_name)s"
+        })
+        t = Table('t', m, Column('x', Integer),
+                        CheckConstraint('x > 5', name='x5'))
+
+    The name of the above constraint will be rendered as ``"ck_t_x5"``.
+    That is, the existing name ``x5`` is used in the naming convention as the
+    ``constraint_name`` token.
+
+    In some situations, such as in migration scripts, we may be rendering
+    the above :class:`.CheckConstraint` with a name that's already been
+    converted.  In order to make sure the name isn't double-modified, the
+    new name is applied using the :func:`.schema.conv` marker.  We can
+    use this explicitly as follows::
+
+
+        m = MetaData(naming_convention={
+            "ck": "ck_%(table_name)s_%(constraint_name)s"
+        })
+        t = Table('t', m, Column('x', Integer),
+                        CheckConstraint('x > 5', name=conv('ck_t_x5')))
+
+    Where above, the :func:`.schema.conv` marker indicates that the constraint
+    name here is final, and the name will render as ``"ck_t_x5"`` and not
+    ``"ck_t_ck_t_x5"``
+
+    .. versionadded:: 0.9.4
+
+    .. seealso::
+
+        :ref:`constraint_naming_conventions`
+
+    """
+
+
 class _defer_name(_truncated_label):
     """mark a name as 'deferred' for the purposes of automated name
     generation.
@@ -3210,6 +3256,8 @@ class _defer_name(_truncated_label):
     def __new__(cls, value):
         if value is None:
             return _NONE_NAME
+        elif isinstance(value, conv):
+            return value
         else:
             return super(_defer_name, cls).__new__(cls, value)