We have not planned to introduce a similar event in RadDataForm for now. However, I believe that there is an easy workaround to tackle this. RadDataForm enables its users to add their own validation errors, through the myRadDataForm.ValidationSummary.Errors property. So, you can catch the constraint exception and "translate" it to your own validation error. Please, be advised that when user-defined validation errors are utilized, a custom Add/Remove errors logic should be implemented, as RadDataForm won't remove them on any circumstances.
the Telerik team
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