從春季卡桑德拉表中取出行

Question

你好，我試圖從卡桑德拉表中取出10行數據。但是每個請求中同樣有10行正在返回。請在這裏看看我的邏輯。並告訴我哪裏做錯了這裏 -

public class CustomerRequestDaoImpl implements CustomerRequestDao 
{ 
    private static Cluster cluster; 

@Resource 
    private CassandraSessionFactory cassandraSessionFactory; 

    /** The ProductsByTagDaoImpl session. */ 
    private Session session; 

    @Override 
    public List<CustomerRequest> getCustomerRequestData(final String productId, final String receiptPeriod) 
    { 

    final int RESULTS_PER_PAGE = 10; 

    session = cassandraSessionFactory.getSession(); 
    final List<CustomerRequest> customerRequestdata = new ArrayList<CustomerRequest>(); 
    try 
    { 
    final PreparedStatement statement = 
     session.prepare("select * from customer_request where product_id = :id and receipt_period = :receiptPeriod"); 

    final BoundStatement boundStatement = new BoundStatement(statement); 
    boundStatement.setFetchSize(RESULTS_PER_PAGE); 
    boundStatement.setString("id", productId); 
    boundStatement.setString("receiptPeriod", receiptPeriod); 
    final ResultSet resultSet = session.execute(boundStatement); 
    final Iterator<Row> iter = resultSet.iterator(); 
    final PagingState nextPage = resultSet.getExecutionInfo().getPagingState(); 

    int remaining = resultSet.getAvailableWithoutFetching(); 
    for (final Row rowdt : resultSet) 
    { 
     customerRequestdata.add(constructCustomerReq(rowdt)); 
     if (--remaining == 0) 
     { 
     break; 
     } 
     } 

    } 
    catch (final Exception e) 
    { 
     e.printStackTrace(); 
    } 
    return customerRequestdata; 
    } 

@PostConstruct 
    public void init() 
    { 
    session = cassandraSessionFactory.getSession(); 
    cluster = session.getCluster(); 

    } 

}

我的表-1 我的表結構： -

CREATE TABLE customer_request (
    product_id varchar PRIMARY KEY, 
    id varchar, 
    receipt_period varchar, 
    delivery_method_status varchar, 
    first_name varchar 
); 

返回應答爲

<e> 
    <deliveryMethodStatus null="true"/> 
    <firstName null="true"/> 
    <id>0b0352f6b3904</id> 
    <lastName Adkin="true"/> 
    <orderId>FORMS8a04e</orderId> 
    <orderItemId>FORMS8a04e-1</orderItemId> 
    <productId>PI_NAME_CHANGE</productId> 
    <receiptPeriod>2016-02-06</receiptPeriod> 
    <receivedDate null="true"/> 
    <requestData null="true"/> 

Answer 1

的幾點意見：

• 您不應該重新準備每一次查詢，這是一個 反模式。準備語句一次，並重新使用它爲每個方法調用

• 告訴你，因爲你的循環爆發的一次remaining
  變量計數將總是返回的
  數據第一頁的源代碼降至0. PagingState對象未使用
  任何地方...

• 您的問題還不清楚Hello am trying to fetch 10 rows of data from Cassandra table. But on each request same 10 row is returning。你想要哪10行？ 第一行 10行？ 10行後的閾值？

  注：尋呼

示例代碼編寫下面的查詢只一次：select * from customer_request where product_id = :id and receipt_period = :receiptPeriod LIMIT :lim並用方法把它傳遞

@Override 
    public List<Tuple2<String,CustomerRequest>> getCustomerRequestData(final String productId, PreparedStatement ps, final String receiptPeriod, String pagingState) 
    { 

    final int PAGE_SIZE = 10; 

    session = cassandraSessionFactory.getSession(); 
    final List<CustomerRequest> customerRequestdata = new ArrayList<CustomerRequest>(); 
    try 
    { 

    final BoundStatement boundStatement = ps.bind(productId, receiptPeriod, PAGE_SIZE); 
    boundStatement.setPagingState(PagingState.fromString(pagingState)); 
    final ResultSet resultSet = session.execute(boundStatement); 
    final Iterator<Row> iter = resultSet.iterator(); 
    final PagingState nextPage = resultSet.getExecutionInfo().getPagingState(); 

    int remaining = resultSet.getAvailableWithoutFetching(); 
    for (final Row rowdt : resultSet) 
    { 
     customerRequestdata.add(constructCustomerReq(rowdt)); 
     if (--remaining == 0) 
     { 
     break; 
     } 
     } 

    } 
    catch (final Exception e) 
    { 
     e.printStackTrace(); 
    } 
    return new Tuple2<>(nextPage.toString(), customerRe); 

請注意使用Tuple2類返回結果列表以及分頁狀態，序列化爲一個字符串，可輕鬆傳遞到前端