Use SQLAlchemy to drop foreign key in DB migrate

A foreign key constraint needs to be removed in order to succeed in the
DB migration. An earlier submitted fix for this uses a mysql drop
statement. I think it's cleaner to use sqlalchemy to do this, as it's
done this way in other version migrations as well. Fix for bug 907254.

Update: IBM from 1928 called, they want their 80 CPL limit
back. - on a more serious note, fixed jenkins PEP8 failure
Update2: Replaced tab by a spaces
Update3: Don't do Foreign Key stuff if the engine is sqlite
Update4: Add myself to the Authors file
Update5: With the correct mail address

Change-Id: Ib021e0ddb2c80ee63888435a9e3761c053534160

Authors

@@ -30,6 +30,7 @@ Chris Behrens <cbehrens@codestud.com>
 Christian Berendt <berendt@b1-systems.de>
 Christopher MacGown <chris@pistoncloud.com>
 Chuck Short <zulcss@ubuntu.com>
+Cor Cornelisse <cor@hyves.nl>
 Cory Wright <corywright@gmail.com>
 Dan Prince <dan.prince@rackspace.com>
 Dan Wendlandt <dan@nicira.com>

nova/db/sqlalchemy/migrate_repo/versions/064_change_instance_id_to_uuid_in_instance_actions.py

@@ -17,6 +17,7 @@
 
 import sqlalchemy
 from sqlalchemy import select, Column, ForeignKey, Integer, String
+from migrate import ForeignKeyConstraint
 
 from nova import log as logging
 
@@ -31,6 +32,7 @@ def _get_table(name):
 
 def upgrade(migrate_engine):
     meta.bind = migrate_engine
+    dialect = migrate_engine.url.get_dialect().name
     instance_actions = _get_table('instance_actions')
     instances = _get_table('instances')
     uuid_column = Column('instance_uuid', String(36),
@@ -48,12 +50,16 @@ def upgrade(migrate_engine):
         uuid_column.drop()
         raise
 
-    if migrate_engine.name == "mysql":
+    if not dialect.startswith('sqlite'):
         try:
-            migrate_engine.execute("ALTER TABLE instance_actions " \
-                "DROP FOREIGN KEY instance_actions_ibfk_1;")
-        except Exception:  # Don't care, just fail silently.
-            pass
+            fkey_name = list(instance_actions.c.instance_id.foreign_keys)[0].\
+                             constraint.name
+            ForeignKeyConstraint(columns=[instance_actions.c.instance_id],
+                                 refcolumns=[instances.c.id],
+                                 name=fkey_name).drop()
+        except Exception:
+            logging.error(_("foreign key constraint couldn't be removed"))
+            raise
 
     instance_actions.c.instance_id.drop()