According to the .NET Framework General Reference: Error Raising and Handling Guidelines exceptions should not be thrown during ‘normal’ operations. Is invalid user input to a web form, say the user enters a duplicate name, considered normal? !! IMPORTANT !!: I’m sure we pretty much all have an opinion on this, please include a reference to a reliable source.
EDIT:
A little more background: I’m questioning the approch to model validation advocated by a book I’m reading. The book is suggesting that you throw a custom exception from a repository when provided with invalid data to save. Now, this seems to me to violate MS guidlines because you are using exceptions as flow control…unless recieving invalid data is consider outside of ‘normal’ operation. I just want to see if there is any further guidance from a reliable source to resolve this.
ANOTHER EDIT:
OK so two and a half years later, I’m moving this repository to a WCF service and using exceptions in this method turned out to be a bad idea. Oh well.
Generally speaking, invalid or ill-formed input is not consider ‘exceptional’ and should be handled using something other than exceptions. But note that this is a guideline – there may well be situations where using exceptions to handle the problem would result in better code.