Re: LIMIT timeframe?

[Jakob Braeuchi]

hi john,
to implement the LIMIT is not too complicated but to make it really work for 
extents is a bit harder.
imo you should use the platform for db-specific stuff.

jakob
[EMAIL PROTECTED] schrieb:
Thank you for your post Jakob.  It sounds like a bit of an effort.  I was 
thinking based on other code perviously posted on the board to get around the 
problem that it might be a bit easier.   I was about to test code people placed 
on the board previously to get around the problem.  I am not sure based on your 
words if it should work?   I will try testing it tonight, but I am a bit 
nervous it might run me into problems in the future now.   Here is the database 
specific code:
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 MySqlStatementGenerator extends SqlGeneratorDefaultImpl
{
    public MySqlStatementGenerator(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;
    }
}

Thank you for your ideas.
JohnE



hi john,
to be hones, my version of the sql-limit stuff was rather basic 
and didn't work 
correctly for extents.
before we can really use the sql-LIMIT we'll have to change ojb to 
use a 
_single_ query for all extents (using the UNION clause). with the 
current 
solution using one select for each extent the LIMIT-clause is not 
useful.
example:

-ojb current version:
select * from person where ... limit ...
select * from musicians where ... limit ...
-future version:
select * from person where ...
union
select * from musicians where ...
limit ...
jakob
[EMAIL PROTECTED] schrieb:
Hey all.  Thank you for great project.
I am very excited about my site having gone live with OJB, but 
there is one aspect of OJB I am really not liking to have to do 
right now -- make it database specific.  It was part of my 
marketing to have the platform I created be non-database specific, 
but that can't be for one reason.

I am looking at all the posts on the board about not having 
LIMIT supported.   I need to do very large table queries but I 
have to add LIMITs specific to MySQL on the query or there would 
be a drastically bad performance issue.

Jakob is your LIMIT code you had working working and do you 
think it might get into 1.0.2 or 1.1?  I know you have bigger fish 
to fry.

I don't know OJB internals well but I am trying to learn so I 
can help in the future. 

JohnE


-----------------------------------------------------------------
----
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]

-------------------------------------------------------------------
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]


---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]

---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]