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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _migrateStorageSchema(self, metadata: MetaData) -> None: """ Initialise the DB This method is called by the platform between the load() and start() calls. There should be no need for a plugin to call this method it's self. :param metadata: the SQLAlchemy metadata for this plugins schema """


        relDir = self._packageCfg.config.storage.alembicDir(require_string)
        alembicDir = os.path.join(self.rootDir, relDir)
        if not os.path.isdir(alembicDir): raise NotADirectoryError(alembicDir)

        self._dbConn = DbConnection(
            dbConnectString=self.platform.dbConnectString,
            metadata=metadata,
            alembicDir=alembicDir,
            enableCreateAll=False
        )

        self._dbConn.migrate()