setting default value

hi,
how can i set a default value in fields from any other tables .while iam using the following code
eg:RouteOpr.SubcontractItem=ProdParametersDim::find(InventDim.inventDimId).Subcontractitem;
the value is stored in the table but my need is the value should not stored but it should be just visible. and it will store when i press the save button pls give some idea .
Thanks & Regards
dhinu.v

Please clarify :

You want to set a default value while creating a new record or in an existing record??

hi ,

yes, but it should not saved automatically it should be saved while clicking the save button

regards

dhinu.v

yes pls give me a solution thanks in advance

You didnt clear my doubt about new record or in existing record???

existing record

thanks