> One of the tasks of a GUI is the validation of user input. The most basic
> validation is the input field size. Validation can be performed by
> attempting to store the data and catching any exceptions, or by limiting the
> input field size at the GUI level (which is, of course, preferred).
>
> However, the standard client->SB->CMP EB->RDBMS model offers no support for
> that:
>
> - the exception model does not work: the container is allowed to delay the
> database write until the end of the transaction, which means that the
> exception occurs *after* all bean instance methods have returned. This
> leaves the client with the nasty job of extracting the SQLException from the
> RemoteException, parsing the vendor-specific message, mapping from the
> database schema to the object level (that was the point of CMP, wasn't it?),
> and finally recovering the beans which have been deleted due to the
> RemoteException thrown.
A costly validation.
>
> - there is no support at the EB level to query the field sizes. Even if I
> were to do this through JDBC, storing global values in EBs is not permitted.
> Even if I knew the field sizes, they would probably be in bytes, not
> characters.
Even if the container were to let you query for this this information
(mapping and DB schema), wouldn't this be expensive to do at runtime?
Secondly, such validation would be applicable only when DB fields are
directly mapped to information in the UI.
- Subrahmanyam
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