def db_sync(engine, version=None): 
  path = os.path.join(os.path.abspath(os.path.dirname(__file__)), 
            'migrate_repo') 
  return oslo_migration.db_sync(engine, path, version, 
                 init_version=INIT_VERSION) 

def db_sync(engine, abs_path, version=None, init_version=0, sanity_check=True): 
  """Upgrade or downgrade a database. 
 
  Function runs the upgrade() or downgrade() functions in change scripts. 
 
  :param engine:    SQLAlchemy engine instance for a given database   //连接数据库 
  :param abs_path:   Absolute path to migrate repository.         //migrate仓库的绝对路径 
  :param version:   Database will upgrade/downgrade until this version. //需要升级或者降级到的版本号，如果不传则默认升级到最新版本 
             If None - database will update to the latest 
             available version. 
  :param init_version: Initial database version               //数据库的初始版本号，会以该初始版本为起点升级 
  :param sanity_check: Require schema sanity checking for all tables    //合理性检查 
  """ 
 
  if version is not None: 
    try: 
      version = int(version) 
    except ValueError: 
      raise exception.DBMigrationError(_("version should be an integer")) 
 
  current_version = db_version(engine, abs_path, init_version) 
  repository = _find_migrate_repo(abs_path) 
  if sanity_check: 
    _db_schema_sanity_check(engine) 
  if version is None or version > current_version: 
    migration = versioning_api.upgrade(engine, repository, version) 
  else: 
    migration = versioning_api.downgrade(engine, repository, 
                       version) 
  if sanity_check: 
    _db_schema_sanity_check(engine) 
 
  return migration 

def db_version(engine, abs_path, init_version): 
  """Show the current version of the repository. 
 
  :param engine: SQLAlchemy engine instance for a given database 
  :param abs_path: Absolute path to migrate repository 
  :param init_version: Initial database version 
  """ 
  repository = _find_migrate_repo(abs_path) 
  try: 
    return versioning_api.db_version(engine, repository) 
  except versioning_exceptions.DatabaseNotControlledError: 
    meta = sqlalchemy.MetaData() 
    meta.reflect(bind=engine) 
    tables = meta.tables 
    if len(tables) == 0 or 'alembic_version' in tables: 
      db_version_control(engine, abs_path, version=init_version) 
      return versioning_api.db_version(engine, repository) 
    else: 
      raise exception.DBMigrationError( 
        _("The database is not under version control, but has " 
         "tables. Please stamp the current version of the schema " 
         "manually.")) 

class Repository(pathed.Pathed): 
  """A project's change script repository""" 
 
  _config = 'migrate.cfg' 
  _versions = 'versions' 
 
  def __init__(self, path): 
    log.debug('Loading repository %s...' % path) 
    self.verify(path) 
    super(Repository, self).__init__(path) 
    self.config = cfgparse.Config(os.path.join(self.path, self._config)) 
    self.versions = version.Collection(os.path.join(self.path, 
                           self._versions)) 
    log.debug('Repository %s loaded successfully' % path) 
    log.debug('Config: %r' % self.config.to_dict()) 

@property 
  def latest(self): 
    """API to :attr:`migrate.versioning.version.Collection.latest`""" 
    return self.versions.latest 
 
  @property 
  def version_table(self): 
    """Returns version_table name specified in config""" 
    return self.config.get('db_settings', 'version_table') 
 
  @property 
  def id(self): 
    """Returns repository id specified in config""" 
    return self.config.get('db_settings', 'repository_id') 

try: 
  return versioning_api.db_version(engine, repository) 
except versioning_exceptions.DatabaseNotControlledError: 
  meta = sqlalchemy.MetaData() 
  meta.reflect(bind=engine) 
  tables = meta.tables 
  if len(tables) == 0 or 'alembic_version' in tables: 
    db_version_control(engine, abs_path, version=init_version) 
    return versioning_api.db_version(engine, repository) 
  else: 
    raise exception.DBMigrationError( 
      _("The database is not under version control, but has " 
       "tables. Please stamp the current version of the schema " 
       "manually.")) 

db_version_control(engine, abs_path, version=init_version)