我正在尝试使用apachebeam cassandraio从cassandra db读取数据，我的需求是从cassandra db装入一个pcollection行，目前我的代码如下所示

PTransform<PBegin,PCollection<Row>>transform=CassandraIO.<Row>read()
   .withHosts(Collections.singletonList("127.0.0.1"))
   .withPort(9042)
   .withKeyspace("\"testDb\"")
   .withMapperFactoryFn(new CassandraRowMapper())
   .withQuery(q)
   .withTable("student")
   .withEntity(Row.class)
   .withCoder(SerializableCoder.of(Row.class));

任何帮助都将不胜感激