Enable native boolean for SQL Server

SQL Server supports what SQLAlchemy calls "native boolean"
with its BIT type, as this type only accepts 0 or 1 and the
DBAPIs return its value as True/False.   So the SQL Server
dialects now enable "native boolean" support, in that a
CHECK constraint is not generated for a :class:`.Boolean`
datatype.  The only difference vs. other native boolean
is that there are no "true" / "false" constants so "1" and
"0" are still rendered here.

Tests are implicit in the existing suites.

Change-Id: I75bbcd549884099fb1a177e68667bf880c40fa7c
Fixes: #4061

1 files changed, 6 insertions, 6 deletions

diff --git a/lib/sqlalchemy/sql/sqltypes.py b/lib/sqlalchemy/sql/sqltypes.py
index fe9a56b6e..d0dbc4881 100644
--- a/lib/sqlalchemy/sql/sqltypes.py
+++ b/lib/sqlalchemy/sql/sqltypes.py
@@ -1603,12 +1603,12 @@ class Boolean(TypeEngine, SchemaType):
         return bool
 
     def literal_processor(self, dialect):
-        if dialect.supports_native_boolean:
-            def process(value):
-                return "true" if value else "false"
-        else:
-            def process(value):
-                return str(1 if value else 0)
+        compiler = dialect.statement_compiler(dialect, None)
+        true = compiler.visit_true(None)
+        false = compiler.visit_false(None)
+
+        def process(value):
+            return true if value else false
         return process
 
     def bind_processor(self, dialect):