ResultSet 异常-在结果集开始之前

我在从 ResultSet对象获取数据时遇到了麻烦。下面是我的代码:

    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)

我做错了什么？

223170 次浏览
小开

You have to do a result.next() before you can access the result. It's a very common idiom to do

ResultSet rs = stmt.executeQuery();
while (rs.next())
{
int foo = rs.getInt(1);
...
}
小开
最佳答案

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);

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

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

You have to call next() before you can start reading values from the first row. beforeFirst puts the cursor before the first row, so there's no data to read.

小开

You need to move the pointer to the first row, before asking for data:

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

It's better if you create a class that has all the query methods, inclusively, in a different package, so instead of typing all the process in every class, you just call the method from that class.

小开

Every answer uses .next() or uses .beforeFirst() and then .next(). But why not this:

result.first();

So You just set the pointer to the first record and go from there. It's available since java 1.2 and I just wanted to mention this for anyone whose ResultSet exists of one specific record.


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