How Forms checks changed records?

Hi!

SQL*Forms is able to give the error message "FRM-40657: Record changed or deleted by another user" when the user changes a field in a queried row. How does SQL*Forms implement this check? Is it an error code that a SELECT FOR UPDATE statement returns? Or does SQL*Forms check each field whether any of them is changed? Or is it an undocumented feature?

I tried to generate a similar situation without SQL*Forms by using two different SQL*Plus sessions, but I didn't receive any return codes which would indicate that the other session had changed the record since it was first select'ed in the first session.

I'm implementing a user interface in C and I would like to implement a similar validity check than SQL*Forms.

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Juhani Jaakola, jaakola_at_cc.helsinki.fi