Hi Karthik,
I cannot open you file because it has a missing ref to your db struct, but as far as i can see you use entities for days/months/years and use id's to connect them to the other entity, why not just use the normal date attribute? Building your system like this will have major impact on building good queries or finding records based on a date..
If you want to use combo's for inputting all separate parts, I think there are forge components to do this much easier.
regards,
Wim