>>> This most cetainly breaks n-tier design. The control UI should not know anything about the business rules. Validation for uniqueness should be done in bizrules object.
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>>I am not a MM programmer, but have a comment or two on the above assertions.
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>>I don't agree that giving a control knowledge of business rules is necessarily a violation of n-tier principals. It only is if the control is solely responsible for enforcing this rule, but duplication of logic often cannot be avoided. Take for example a web page that uses client-side script to ensure that the user enters all of the fields on a form. The data tier should have rules in place to ensure that all of the required fields are present, but for the sake of interface speed and conservation of server resources I see no problem with duplicating this logic in the client.
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>Normally I'd agree with you, but I feel in this situation the lines are being crossed. I have no problem doing simple client side validataion, although purists would say even this is breaking the n-tier model. Here, however, we have a text box requering a lookup view, which really should be the job of the BO.

If the textbox bypasses the BO to get the data, then I agree. I was taking exception to the following blanket statement:

"The control UI should not know anything about the business rules. "