nl_tokens: Performs a single - version database migration to the schema described by the provided database schema descriptor .
pl_tokens: function migrateDatabaseVersion ( nativeDatabase , nativeTransaction , descriptor ) { let fetchPromise if ( descriptor . fetchBefore && descriptor . fetchBefore . length ) { let fetcher = <mask> RecordFetcher ( ) let objectStores = normalizeFetchBeforeObjectStores ( descriptor . fetchBefore ) fetchPromise = fetcher . fetchRecords ( nativeTransaction , objectStores ) } else { fetchPromise = PromiseSync . resolve ( { } ) } return fetchPromise . then ( ( recordsMap ) => { let versionMigrator = new DatabaseVersionMigrator ( nativeDatabase , nativeTransaction , descriptor . objectStores ) return versionMigrator . executeMigration ( descriptor . after || ( ( ) => { } ) , recordsMap ) } ) }