Gridview and ObjectDataSource with Custom object : update problem

Hello,
I'm using a gridview with objectdatasource and custom objects collections
SELECT/INSERT/UPDATE/DELETE methods are using custom objects as parameters.
This is working fine. But I have a problem with the object that is passed
back to the update method. It contains some of the properties of the
original object sent during the SELECT method, but is missing others ! How
can I ensure that all original object properties not modified are also set
in the object given to the update mehod ?
TIA.


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