Add schema downgrade action for the web app database. (#114)

knowledge_repo/app/app.py

@@ -288,6 +288,10 @@ def db_upgrade(self):
         with self.app_context():
             command.upgrade(self._alembic_config, "head")
 
+    def db_downgrade(self, revision):
+        with self.app_context():
+            command.downgrade(self._alembic_config, revision)
+
     def db_migrate(self, message, autogenerate=True):
         with self.app_context():
             command.revision(self._alembic_config, message=message, autogenerate=autogenerate)

scripts/knowledge_repo

@@ -210,6 +210,12 @@ db_upgrade.add_argument('-c', '--config', default=None, help="The config file fr
 db_upgrade.add_argument('-m', '--message', help="The message to use for the database revision.")
 db_upgrade.add_argument('--autogenerate', action='store_true', help="Whether alembic should automatically populate the migration script.")
 
+db_downgrade = subparsers.add_parser('db_downgrade', help='Downgrade the database to the schema identified by a revision number.')
+db_downgrade.set_defaults(action='db_downgrade')
+db_downgrade.add_argument('revision', help="The target database revision. Use '-1' for the previous version.")
+db_downgrade.add_argument('-db', '--dburi', help='The SQLAlchemy database uri.')
+db_downgrade.add_argument('-c', '--config', default=None, help="The config file from which to read server configuration.")
+
 reindex = subparsers.add_parser('reindex', help='Update the index, updating all posts even if they exist in the database already; but will not lose post views and other usage metadata.')
 reindex.set_defaults(action='reindex')
 reindex.add_argument('-db', '--dburi', help='The SQLAlchemy database uri.')
@@ -332,6 +338,10 @@ elif args.action == 'db_upgrade':
     app = repo.get_app(db_uri=args.dburi, debug=args.debug, config=args.config)
     app.db_upgrade()
 
+elif args.action == 'db_downgrade':
+    app = repo.get_app(db_uri=args.dburi, debug=args.debug, config=args.config)
+    app.db_downgrade(revision=args.revision)
+
 elif args.action == 'db_migrate':
     app = repo.get_app(debug=args.debug, db_uri=args.dburi)
     app.db_migrate(args.message, autogenerate=args.autogenerate)