use Table._columns to remove columns (addresses #112)

- add SQLA_07 predicate in migrate/changeset/__init__.py

- use Table._columns instead of Table.c when removing columns in
  migrate/changeset/schema.py

2 files changed, 6 insertions, 2 deletions

diff --git a/migrate/changeset/__init__.py b/migrate/changeset/__init__.py
index 7a12643..fa3387d 100644
--- a/migrate/changeset/__init__.py
+++ b/migrate/changeset/__init__.py
@@ -14,6 +14,7 @@ warnings.simplefilter('always', DeprecationWarning)
 
 _sa_version = tuple(int(re.match("\d+", x).group(0)) for x in _sa_version.split("."))
 SQLA_06 = _sa_version >= (0, 6)
+SQLA_07 = _sa_version >= (0, 7)
 
 del re
 del _sa_version
diff --git a/migrate/changeset/schema.py b/migrate/changeset/schema.py
index 75cd3fd..1bd3fc0 100644
--- a/migrate/changeset/schema.py
+++ b/migrate/changeset/schema.py
@@ -11,7 +11,7 @@ from sqlalchemy.schema import ForeignKeyConstraint
 from sqlalchemy.schema import UniqueConstraint
 
 from migrate.exceptions import *
-from migrate.changeset import SQLA_06
+from migrate.changeset import SQLA_06, SQLA_07
 from migrate.changeset.databases.visitor import (get_engine_visitor,
                                                  run_single_visitor)
 
@@ -590,7 +590,10 @@ populated with defaults
         table.constraints = table.constraints - to_drop
         
         if table.c.contains_column(self):
-            table.c.remove(self)
+            if SQLA_07:
+                table._columns.remove(self)
+            else:
+                table.c.remove(self)
 
     # TODO: this is fixed in 0.6
     def copy_fixed(self, **kw):