Mail list archive seems not to be working properly, otherwise I'd point
you to previous postings....
1. Use query.setStartAtIndex() and setEndAtIndex() to specify which
records you actually want to retrieve in the query.
2. Implement the functionality that translates these parameters into
something your database can understand by providing your own
SqlGenerator class and pointing to it OJB.properties.
For example, I did it like this for PostgreSQL:
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: Theo Niemeijer [mailto:[EMAIL PROTECTED]
Sent: Friday, March 21, 2003 5:08 AM
To: OJB Users List
Subject: Webapp google queries: What is a good way to present multiple
web pages with query results ?
Maybe someone has a suggestion for me:
The problem I am facing is that a user can have a very long list of
results, and that list of items is presented in multiple pages of HTML
(like Google :->)
Let's assume that a query will have 10.000 resultitems, and I display 20
items per HTML page with a Next and a Previous button.
- When I use a QueryIterator and for each next page just iterate 20
items further
I assume that it will tie the database connection up for quite some
time,
and I can not even be sure that the user will ask for the next page of
results !
- When I just get all the items in a large collection it will cost me a
lot of "materialisation" time and a lot of memory.
- When I only ask for the object identities and then get the pages by
making a query
for 20 identies in a kind of "select ... where id's in [....]" then the
user would have to wait for that query, but it may be mcuh faster than
the original query.
- When I just re-submit the query for each page, and iterate to the
correct 20 items then the user would have to wait for the query each
time, but it may actually be fast because only 20 items would be
"materialised".
Anyone having experience with this problem and wanting to share best
practices ?
Regards,
Theo Niemeijer
---------------------------------------------------------------------
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]
