Fix ibmdb2 index name handling

The ibmdb2 code calls _index_identifier() when it handles index name. This
method only exists from sqlalchemy 0.6.5 to 0.7.*. Nova code change
https://review.openstack.org/#/c/153123/ attempts to drop a db constraint and
it fails to sync nova db with sqlalchemy 0.9.8 running against db2. Need to let
ibmdb2 code identify sqlalchemy version and call the correct method to handle
index name.

Closes-Bug: 1428477

Change-Id: Ie6333f9cea0209c1ea290356873a1a1bcf409bed

migrate/changeset/databases/ibmdb2.py

@@ -118,10 +118,28 @@ def _rename_table(self, table):
         self.append("RENAME TABLE %s " % self.preparer.format_table(table))
 
     def visit_index(self, index):
-        old_name = self.preparer.quote(self._index_identifier(index.name),
-                                       index.quote)
-        new_name = self.preparer.quote(self._index_identifier(index.new_name),
-                                       index.quote)
+        if hasattr(self, '_index_identifier'):
+            # SA >= 0.6.5, < 0.8
+            old_name = self.preparer.quote(
+                self._index_identifier(index.name), index.quote)
+            new_name = self.preparer.quote(
+                self._index_identifier(index.new_name), index.quote)
+        else:
+            # SA >= 0.8
+            class NewName(object):
+                """Map obj.name -> obj.new_name"""
+                def __init__(self, index):
+                    self.name = index.new_name
+                    self._obj = index
+
+                def __getattr__(self, attr):
+                    if attr == 'name':
+                        return getattr(self, attr)
+                    return getattr(self._obj, attr)
+
+            old_name = self._prepared_index_name(index)
+            new_name = self._prepared_index_name(NewName(index))
+
         self.append("RENAME INDEX %s TO %s" % (old_name, new_name))
         self.execute()
         self.append("COMMIT")
@@ -293,8 +311,14 @@ def _visit_constraint(self, constraint):
                     constraint.exclude_nulls = True
                     break
         if getattr(constraint, 'exclude_nulls', None):
-            index_name = self.preparer.quote(
-                self._index_identifier(constraint.name), constraint.quote)
+            if hasattr(self, '_index_identifier'):
+                # SA >= 0.6.5, < 0.8
+                index_name = self.preparer.quote(
+                    self._index_identifier(constraint.name),
+                    constraint.quote)
+            else:
+                # SA >= 0.8
+                index_name = self._prepared_index_name(constraint)
             sql = 'DROP INDEX %s ' % index_name
         else:
             sql = self.process(DropConstraint(constraint,