结果集异常 - 在结果集开始之前 [英] ResultSet exception - before start of result set

问题描述

我无法从 ResultSet 对象.这是我的代码:

I'm having trouble getting data from a ResultSet object. Here is my code:

    String sql = "SELECT type FROM node WHERE nid = ?";
    PreparedStatement prep = conn.prepareStatement(sql);
    int meetNID = Integer.parseInt(node.get(BoutField.field_meet_nid));
    prep.setInt(1, meetNID);

    ResultSet result = prep.executeQuery();
    result.beforeFirst();
    String foundType = result.getString(1);

    if (! foundType.equals("meet")) {
        throw new IllegalArgumentException(String.format("Node %d must be of type 'meet', but was %s", meetNID, foundType));
    }

错误跟踪:

Exception in thread "main" java.sql.SQLException: Before start of result set
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1072)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:986)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:981)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
    at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:841)
    at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5656)
    at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5576)
    at nth.cumf3.nodeImport.Validator.validate(Validator.java:43)
    at nth.cumf3.nodeImport.Main.main(Main.java:38)

我在这里做错了什么?

推荐答案

基本上，您将光标定位在第一行之前，然后请求数据.您需要将光标移动到第一行.

Basically you are positioning the cursor before the first row and then requesting data. You need to move the cursor to the first row.

 result.next();
 String foundType = result.getString(1);

通常在 if 语句或循环中执行此操作.

It is common to do this in an if statement or loop.

if(result.next()){
   foundType = result.getString(1);
}

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