ResultSet exception - before start of result set

Question

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));
    }

The error trace:

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)

What am I doing wrong here?

Answer 1

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);
}

Answer 2

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.

Answer 3

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);
   ...
}

Answer 4

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.

Answer 5

最好创建一个包含所有查询方法的类，包括在不同的包中，这样就不必在每个类中键入所有过程，而只需从该类中调用该方法。

Answer 6

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

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