Re: Limiting a number of rows returned

[Jakob Braeuchi]

hi max,

anyone is invited to contribute...

jakob

Max Vesely wrote:

Thanks, Scott. 

Would database implementation be the right place for this code? 

If yes, is anyone working on it? 

If not, Can someone like me contribute to OJB framework?

Thank, you.
Max.
-----Original Message-----
From: Scott Howlett [mailto:[EMAIL PROTECTED] 
Sent: Wednesday, February 26, 2003 10:30 PM
To: OJB Users List
Subject: RE: Limiting a number of rows returned

I implemented this functionality for PostgreSQL.

I subclassed SqlGeneratorDefaultImpl to provide the functionality and then
pointed to my subclass in OJB.properties.
My OJB.properties entry is:

SqlGeneratorClass=PostgreSqlStatementGenerator

My subclass code is:

import org.apache.ojb.broker.accesslayer.sql.SqlGeneratorDefaultImpl;
import org.apache.ojb.broker.metadata.ClassDescriptor;
import org.apache.ojb.broker.platforms.Platform;
import org.apache.ojb.broker.query.Query;
public class PostgreSqlStatementGenerator extends SqlGeneratorDefaultImpl {

   public SqlStatementGenerator(Platform pf) {
       super(pf);
   }
   public String getPreparedSelectStatement(
       Query query,
       ClassDescriptor cld) {
       String result = super.getPreparedSelectStatement(query, cld);
       return addOffsetLimit(query, result);
   }
   public String getSelectStatementDep(Query query, ClassDescriptor
cld) {
       String result = super.getSelectStatementDep(query, cld);
       return addOffsetLimit(query, result);
   }
   private String addOffsetLimit(Query q, String stmt) {
       int startIndex = q.getStartAtIndex();
       int endIndex = q.getEndAtIndex();
       if (endIndex > 0) {
           if (startIndex < 0 || startIndex >= endIndex) {
               startIndex = 0;
           }
           stmt += " LIMIT " + (endIndex - startIndex);
       }
       if (startIndex > 0) {
           stmt += " OFFSET " + startIndex;
       }
       return stmt;
   }
}

Hope that helps,
Scott Howlett
-----Original Message-----
From: Max Vesely [mailto:[EMAIL PROTECTED] 
Sent: Wednesday, February 26, 2003 10:27 PM
To: [EMAIL PROTECTED]
Subject: Limiting a number of rows returned

Hi,

  Does anyone know how to limit a number of rows returned from database
using OJB?  

Most of the database engines implement custom keywords to limit a number of
rows for select statement (top, limit, rownum () < .....), OJB Query
interface has methods in it to set EndAt and StartAt indexes as well as the
size of resultset returned but setting them doesn't really help. The
database engine I'm using is HSQLDB.
Thank, you in advance.

Max.

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