Subreport linking using javabean datasource

Hi,

I have one master report and one subreport.I am feeding a bean object to my subreport to retreive certain fields which is coming fine when i run the subreport.My problem is when i link the subreport with my main report i cannot retreive proper data.I understand that the problem lies in the "datasource expression" which i am not clear of what exactly to use during the subreport wizard creation.I am using i-report 3.7 and i have given the classpath for the jar for the bean object and the connection\datasourceset for javabeans is also fine.My doubt is only in the connection type and the datasource expression to use in the subreport creation wizard.Please help me out with proper steps.Thanks.