Re: [OJB-developers] cursor control

[Thomas M. <tho...@ho...>]

Hi Matthew,

Matthew Baird wrote:

 > I'm currently working on some rudimentary cursor control for ODMG.


good idea!

 >I want to
 > outline my approach and solicite some feedback:
 >
 > 1. Creation of an EnhancedOQLQuery interface that includes:
 > 		void create(String queryString, int startAtIndex, int
 > endAtIndex) throws QueryInvalidException;
 > 	int fullSize();
 >


ACK


 > 2. have OQLQueryImpl implement both OQLQuery and EnhancedOQLQuery.
 >


ACK


 > 3. create(String, int, int) creates a query that uses the resultsets
 > underlying cursor to return results starting at startAtIndex, and 
ending at
 > endAtIndex, thus being the most efficient way to return results for a 
"page"
 > of data.


ACK
How does it work internally? Are you using
PersistenceBroker.getIteratorByQuery(...)? How do you manage to start at
a given index?


 >
 > 4. fullSize() returns the actual size the query returns, based on 
using the
 > underlying resultsets cursor to move rows instead of iterating 
through. If
 > you have a start and end index, it will still return how many rows 
the query
 > would have returned if you hadn't limited it.


ACK


 >
 > GOALS:
 > - Backward compatibility. If you don't want this functionality, don't 
change
 > your code and it will continue to work exactly as before.
 > - Maximum efficiency for building a paged result set of many items. 
In our
 > application we have to display the classic (1-10 of 100,002,040) paged
 > result set. If we had to iterate through the results materializing 
objects
 > (even proxies) it could take all day to display one page. Using the 
query to
 > limit the number of returned objects or just displaying 1-10 of LOTS! 
Is not
 > an option as the last number is important for the user.
 > - improve performance of OJB by only using scrollable resultsets if 
the user
 > needs them.
 >
 > I currently DO NOT like the names I made for getting the size on the
 > underlying query. Please comment on what they should be.


What about something like:
rowCount()
elementCount()
actualRowCount()
actualElementCount()


 >
 > I have a full test suite for the implementation that stresses every
 > combination of startAtIndex/endAtIndex and size.
 >


that's a real plus!

I think a paging query is a very useful thing not only for the ODMG
implementation but also for the PersistenceBroker.


cheers,

Thomas


 > Please send me your thoughts. Thanks
 > Matthew
 >
 > _______________________________________________________________
 >
 > Don't miss the 2002 Sprint PCS Application Developer's Conference
 > August 25-28 in Las Vegas -- http://devcon.sprintpcs.com/adp/index.cfm
 >
 > _______________________________________________
 > Objectbridge-developers mailing list
 > Obj...@li...
 > https://lists.sourceforge.net/lists/listinfo/objectbridge-developers
 >
 >
 >
 >