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Diffstat (limited to 'mediagoblin/db/migration_tools.py')
| -rw-r--r-- | mediagoblin/db/migration_tools.py | 276 |
1 files changed, 276 insertions, 0 deletions
diff --git a/mediagoblin/db/migration_tools.py b/mediagoblin/db/migration_tools.py new file mode 100644 index 00000000..c0c7e998 --- /dev/null +++ b/mediagoblin/db/migration_tools.py @@ -0,0 +1,276 @@ +# GNU MediaGoblin -- federated, autonomous media hosting +# Copyright (C) 2011, 2012 MediaGoblin contributors. See AUTHORS. +# +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU Affero General Public License as published by +# the Free Software Foundation, either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU Affero General Public License for more details. +# +# You should have received a copy of the GNU Affero General Public License +# along with this program. If not, see <http://www.gnu.org/licenses/>. + +from mediagoblin.tools.common import simple_printer +from sqlalchemy import Table + +class TableAlreadyExists(Exception): + pass + + +class MigrationManager(object): + """ + Migration handling tool. + + Takes information about a database, lets you update the database + to the latest migrations, etc. + """ + + def __init__(self, name, models, migration_registry, session, + printer=simple_printer): + """ + Args: + - name: identifier of this section of the database + - session: session we're going to migrate + - migration_registry: where we should find all migrations to + run + """ + self.name = unicode(name) + self.models = models + self.session = session + self.migration_registry = migration_registry + self._sorted_migrations = None + self.printer = printer + + # For convenience + from mediagoblin.db.models import MigrationData + + self.migration_model = MigrationData + self.migration_table = MigrationData.__table__ + + @property + def sorted_migrations(self): + """ + Sort migrations if necessary and store in self._sorted_migrations + """ + if not self._sorted_migrations: + self._sorted_migrations = sorted( + self.migration_registry.items(), + # sort on the key... the migration number + key=lambda migration_tuple: migration_tuple[0]) + + return self._sorted_migrations + + @property + def migration_data(self): + """ + Get the migration row associated with this object, if any. + """ + return self.session.query( + self.migration_model).filter_by(name=self.name).first() + + @property + def latest_migration(self): + """ + Return a migration number for the latest migration, or 0 if + there are no migrations. + """ + if self.sorted_migrations: + return self.sorted_migrations[-1][0] + else: + # If no migrations have been set, we start at 0. + return 0 + + @property + def database_current_migration(self): + """ + Return the current migration in the database. + """ + # If the table doesn't even exist, return None. + if not self.migration_table.exists(self.session.bind): + return None + + # Also return None if self.migration_data is None. + if self.migration_data is None: + return None + + return self.migration_data.version + + def set_current_migration(self, migration_number=None): + """ + Set the migration in the database to migration_number + (or, the latest available) + """ + self.migration_data.version = migration_number or self.latest_migration + self.session.commit() + + def migrations_to_run(self): + """ + Get a list of migrations to run still, if any. + + Note that this will fail if there's no migration record for + this class! + """ + assert self.database_current_migration is not None + + db_current_migration = self.database_current_migration + + return [ + (migration_number, migration_func) + for migration_number, migration_func in self.sorted_migrations + if migration_number > db_current_migration] + + + def init_tables(self): + """ + Create all tables relative to this package + """ + # sanity check before we proceed, none of these should be created + for model in self.models: + # Maybe in the future just print out a "Yikes!" or something? + if model.__table__.exists(self.session.bind): + raise TableAlreadyExists( + u"Intended to create table '%s' but it already exists" % + model.__table__.name) + + self.migration_model.metadata.create_all( + self.session.bind, + tables=[model.__table__ for model in self.models]) + + def create_new_migration_record(self): + """ + Create a new migration record for this migration set + """ + migration_record = self.migration_model( + name=self.name, + version=self.latest_migration) + self.session.add(migration_record) + self.session.commit() + + def dry_run(self): + """ + Print out a dry run of what we would have upgraded. + """ + if self.database_current_migration is None: + self.printer( + u'~> Woulda initialized: %s\n' % self.name_for_printing()) + return u'inited' + + migrations_to_run = self.migrations_to_run() + if migrations_to_run: + self.printer( + u'~> Woulda updated %s:\n' % self.name_for_printing()) + + for migration_number, migration_func in migrations_to_run(): + self.printer( + u' + Would update %s, "%s"\n' % ( + migration_number, migration_func.func_name)) + + return u'migrated' + + def name_for_printing(self): + if self.name == u'__main__': + return u"main mediagoblin tables" + else: + # TODO: Use the friendlier media manager "human readable" name + return u'media type "%s"' % self.name + + def init_or_migrate(self): + """ + Initialize the database or migrate if appropriate. + + Returns information about whether or not we initialized + ('inited'), migrated ('migrated'), or did nothing (None) + """ + assure_migrations_table_setup(self.session) + + # Find out what migration number, if any, this database data is at, + # and what the latest is. + migration_number = self.database_current_migration + + # Is this our first time? Is there even a table entry for + # this identifier? + # If so: + # - create all tables + # - create record in migrations registry + # - print / inform the user + # - return 'inited' + if migration_number is None: + self.printer(u"-> Initializing %s... " % self.name_for_printing()) + + self.init_tables() + # auto-set at latest migration number + self.create_new_migration_record() + + self.printer(u"done.\n") + self.set_current_migration() + return u'inited' + + # Run migrations, if appropriate. + migrations_to_run = self.migrations_to_run() + if migrations_to_run: + self.printer( + u'-> Updating %s:\n' % self.name_for_printing()) + for migration_number, migration_func in migrations_to_run: + self.printer( + u' + Running migration %s, "%s"... ' % ( + migration_number, migration_func.func_name)) + migration_func(self.session) + self.set_current_migration(migration_number) + self.printer('done.\n') + + return u'migrated' + + # Otherwise return None. Well it would do this anyway, but + # for clarity... ;) + return None + + +class RegisterMigration(object): + """ + Tool for registering migrations + + Call like: + + @RegisterMigration(33) + def update_dwarves(database): + [...] + + This will register your migration with the default migration + registry. Alternately, to specify a very specific + migration_registry, you can pass in that as the second argument. + + Note, the number of your migration should NEVER be 0 or less than + 0. 0 is the default "no migrations" state! + """ + def __init__(self, migration_number, migration_registry): + assert migration_number > 0, "Migration number must be > 0!" + assert migration_number not in migration_registry, \ + "Duplicate migration numbers detected! That's not allowed!" + + self.migration_number = migration_number + self.migration_registry = migration_registry + + def __call__(self, migration): + self.migration_registry[self.migration_number] = migration + return migration + + +def assure_migrations_table_setup(db): + """ + Make sure the migrations table is set up in the database. + """ + from mediagoblin.db.models import MigrationData + + if not MigrationData.__table__.exists(db.bind): + MigrationData.metadata.create_all( + db.bind, tables=[MigrationData.__table__]) + + +def inspect_table(metadata, table_name): + """Simple helper to get a ref to an already existing table""" + return Table(table_name, metadata, autoload=True, + autoload_with=metadata.bind) |