ResultSet exception - before start of result set
JavaJdbcJava Problem Overview
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?
Java Solutions
Solution 1 - Java
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);
}
Solution 2 - Java
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.
Solution 3 - Java
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);
...
}
Solution 4 - Java
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.
Solution 5 - Java
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.
Solution 6 - Java
You need to move the pointer to the first row, before asking for data:
result.beforeFirst();
result.next();
String foundType = result.getString(1);