Introduce basic primitives for alembic support:

- Reflection works at a basic level but upgrades/downgrades fail to
   read the expected data from alembic_versions table
- It's not clear how to make reflection capture the scale and precision
   of DECIMAL() column types.

Signed-off-by: Jesse Whitehouse <[email protected]>

Author: Jesse Whitehouse

src/databricks/sqlalchemy/dialect/__init__.py

@@ -14,6 +14,15 @@
 )
 from databricks.sqlalchemy.dialect.compiler import DatabricksTypeCompiler
 
+try:
+    import alembic
+except ImportError:
+    pass
+else:
+    from alembic.ddl import DefaultImpl
+    class DatabricksImpl(DefaultImpl):
+        __dialect__ = 'databricks'
+
 
 class DatabricksDialect(default.DefaultDialect):
     """This dialect implements only those methods required to pass our e2e tests"""
@@ -111,9 +120,14 @@ def get_columns(self, connection, table_name, schema=None, **kwargs):
 
         for col in resp:
 
+          if "DECIMAL(" in col.TYPE_NAME:
+            _this_type = types.DECIMAL
+          else:
+            _this_type = _type_map.get(col.TYPE_NAME.lower())
+
             this_column = {
                 "name": col.COLUMN_NAME,
-                "type": _type_map.get(col.TYPE_NAME.lower()),
+                "type": _this_type,
                 "nullable": bool(col.NULLABLE),
                 "default": col.COLUMN_DEF,
                 "autoincrement": False if col.IS_AUTO_INCREMENT == "NO" else True,