import logging
log = logging.getLogger(__name__)
class MigrationMeta(type):
'''Metaclass providing a registry of migrations.
If the class-level variable _current_migrations_module is
defined, then migrations will be registered according to that
module and their declared version. (The migrate command
sets this module according to the migration's entry point name.)
'''
def __init__(cls, name, bases, dct):
if cls._current_migrations_module is None: return
cls.migrations_registry[
cls._current_migrations_module, cls.version] = cls
cls.module = cls._current_migrations_module
def get(cls, module, version):
'''Load a Migration class from the registry'''
return cls.migrations_registry[module, version]
def latest_versions(cls):
result = {}
for k,v in cls.migrations_registry:
if result.get(k, -1) < v:
result[k] = v
return result
class Migration(object):
__metaclass__ = MigrationMeta
version = 0
module = None # filled in automatically by Metaclass
migrations_registry = {}
_current_migrations_module = None
def __init__(self, session):
self.session = session
def requires(self):
'''Returns a list of requirements that must be met before upgrading to
this migration. By default, returns the previous-versioned migration'''
return [ (self.module, self.version-1) ]
def up(self):
'''Upgrade to a new schema version'''
raise NotImplementedError, 'up'
def down(self):
'''Downgrade from this schema version (undo an 'up') '''
raise NotImplementedError, 'down'
def ensure_index(self, cls, fields, **kwargs):
'''Ensures that a particular index has been created in the DB'''
self.session.ensure_index(cls, fields, **kwargs)
def drop_index(self, cls, fields):
'''Ensures that a particular index has been dropped from the DB'''
self.session.drop_index(cls, fields)
def set_indexes(self, cls):
'''Ensures that a the only indexes on a class are those defined in its
__mongometa__ attribute.'''
self.session.drop_indexes(cls)
self.session.ensure_indexes(cls)