Question

我在PostgreSQL数据库上使用JDBC。当我在结果集中查询实体时，它返回5行。与该实体相关的是另一个实体，当我在上面的结果集中使用一行时，我会查询该实体。当我执行此查询时，上述结果集将被关闭。

这意味着它一次只能在1个连接上激活1个结果集。

以前，相同的代码适用于Oracle DB服务器。

是否需要请求DB管理员配置服务器以允许多个结果集？或者在代码中做一些改变？或者在postgre中不可能这样做？以下是有关详细信息的代码：

    Connection conn = PTSConnection.getConnection();

    Statement stmt = conn.createStatement();

    ResultSet lines = stmt.executeQuery("SELECT LINEID,STARTSTOPID,ENDSTOPID FROM LINES"); **//first resultset is active**

    while (lines.next()){
        int lineId= lines.getInt(1);
        Stop ss = StopStorage.getByID(lines.getInt(2));
        Stop es = StopStorage.getByID(lines.getInt(3));
        ResultSet stops = stmt.executeQuery("SELECT STOPID FROM STOPSINLINES WHERE LINEID=" + lineId); **//first resultset dies**

        List<Stop> lineStops = new ArrayList<Stop>();
        while(stops.next()){
            Stop stop = StopStorage.getByID(stops.getInt(1));
            lineStops.add(stop);
        }
        stops.close();

        Line aLine = null;

        ResultSet emergencyLine = stmt.executeQuery("SELECT CAUSE, STARTTIME, ENDTIME FROM EMERGENCYLINES WHERE LINEID =" + lineId);
        if(emergencyLine.next()){
            String cause = emergencyLine.getString(1);
            Time startTime = emergencyLine.getTime(2);
            Time endTime = emergencyLine.getTime(3);

            aLine = new EmergencyLine(ss, es, cause, startTime, endTime, (Stop[]) lineStops.toArray(new Stop[lineStops.size()]));
        } else {
            aLine = new Line(ss, es, (Stop[]) lineStops.toArray(new Stop[lineStops.size()]));
        }

        emergencyLine.close();

        LineRepository.getInstance().addLine(aLine);
    }

    lines.close();

Answer 1

原因不是您在同一连接上使用两个结果集，而是重新使用相同的Statement对象进行新查询。当您在Statement实例上运行executeQuery（）时，任何以前的结果都将被关闭（我很惊讶您的代码确实与Oracle一起工作...）

在执行第二个查询之前，只需创建一个新的Statement对象：

Statement stmt = conn.createStatement();
Statement nestedStmt = conn.createStatement();

ResultSet lines = stmt.executeQuery("SELECT LINEID,STARTSTOPID,ENDSTOPID FROM LINES"); **//first resultset is active**

while (lines.next()){
  ... 
    ResultSet stops = nestedStmt.executeQuery("SELECT STOPID FROM STOPSINLINES WHERE LINEID=" + lineId); **//first resultset dies**
    List lineStops = new ArrayList();
    while(stops.next()){
        Stop stop = StopStorage.getByID(stops.getInt(1));
        lineStops.add(stop);
    }
    stops.close();

    ...
    ResultSet emergencyLine = nestedStmt.executeQuery("SELECT CAUSE, STARTTIME, ENDTIME FROM EMERGENCYLINES WHERE LINEID =" + lineId);
    if(emergencyLine.next()){
        String cause = emergencyLine.getString(1);

    ....
    }
    emergencyLine.close();

并且不要正确关闭所有语句和结果集！

如何在POSTGRES JDBC中使用多个结果集？

1 个答案: