Use new mxODBC 3.3.4 varbinary null symbol

Use new mxODBC 3.3.4 varbinary null symbol with VARBINARY
data types when value is None(based on similar change to pyodbc).
Fix a test to pass on mxODBC starting w 3.3.3 version

Change-Id: Id703ecb51ebc5db149c81fef124f673433606c7f
Pull-request: https://bitbucket.org/zzzeek/sqlalchemy/pull-requests/58

3 files changed, 38 insertions, 1 deletions

diff --git a/doc/build/changelog/changelog_11.rst b/doc/build/changelog/changelog_11.rst
index cb42d61a4..27513e569 100644
--- a/doc/build/changelog/changelog_11.rst
+++ b/doc/build/changelog/changelog_11.rst
@@ -22,6 +22,14 @@
     :version: 1.1.0b1
 
     .. change::
+        :tags: bug, mssql
+        :pullreq: bitbucket:58
+
+        Adjustments to the mxODBC dialect to make use of the ``BinaryNull``
+        symbol when appropriate in conjunction with the ``VARBINARY``
+        data type.  Pull request courtesy Sheila Allen.
+
+    .. change::
         :tags: change, orm
         :tickets: 3394
 
diff --git a/lib/sqlalchemy/dialects/mssql/mxodbc.py b/lib/sqlalchemy/dialects/mssql/mxodbc.py
index 5e20ed11b..e968920bf 100644
--- a/lib/sqlalchemy/dialects/mssql/mxodbc.py
+++ b/lib/sqlalchemy/dialects/mssql/mxodbc.py
@@ -48,6 +48,7 @@ from ...connectors.mxodbc import MxODBCConnector
 from .pyodbc import MSExecutionContext_pyodbc, _MSNumeric_pyodbc
 from .base import (MSDialect,
                    MSSQLStrictCompiler,
+                   VARBINARY,
                    _MSDateTime, _MSDate, _MSTime)
 
 
@@ -76,6 +77,30 @@ class _MSTime_mxodbc(_MSTime):
         return process
 
 
+class _VARBINARY_mxodbc(VARBINARY):
+
+    """
+    mxODBC Support for VARBINARY column types.
+
+    This handles the special case for null VARBINARY values,
+    which maps None values to the mx.ODBC.Manager.BinaryNull symbol.
+    """
+
+    def bind_processor(self, dialect):
+        if dialect.dbapi is None:
+            return None
+
+        DBAPIBinary = dialect.dbapi.Binary
+
+        def process(value):
+            if value is not None:
+                return DBAPIBinary(value)
+            else:
+                # should pull from mx.ODBC.Manager.BinaryNull
+                return dialect.dbapi.BinaryNull
+        return process
+
+
 class MSExecutionContext_mxodbc(MSExecutionContext_pyodbc):
     """
     The pyodbc execution context is useful for enabling
@@ -103,6 +128,8 @@ class MSDialect_mxodbc(MxODBCConnector, MSDialect):
         sqltypes.DateTime: _MSDateTime,
         sqltypes.Date: _MSDate_mxodbc,
         sqltypes.Time: _MSTime_mxodbc,
+        VARBINARY: _VARBINARY_mxodbc,
+        sqltypes.LargeBinary: _VARBINARY_mxodbc,
     }
 
     def __init__(self, description_encoding=None, **params):
diff --git a/test/dialect/mssql/test_types.py b/test/dialect/mssql/test_types.py
index 37c0e7060..f13e26c67 100644
--- a/test/dialect/mssql/test_types.py
+++ b/test/dialect/mssql/test_types.py
@@ -442,7 +442,9 @@ class TypeRoundTripTest(
     def teardown(self):
         metadata.drop_all()
 
-    @testing.fails_on_everything_except('mssql+pyodbc')
+    @testing.fails_on_everything_except(
+        'mssql+pyodbc',
+        'mssql+mxodbc')
     def test_decimal_notation(self):
         numeric_table = Table(
             'numeric_table', metadata,