Business Validation Logic Code Smell

Question

Consider the following code:

partial class OurBusinessObject {
    partial void OnOurPropertyChanged() {
        if(ValidateOurProperty(this.OurProperty) ==          


        

Answer 1

I think I have to agree with you. This could definitely lead to issues where the logic unexpectedly returns to the defaults, which could be very difficult to debug.

At the very least, this behavior should be logged, but this seems more like a case for throwing an exception.

Answer 2

I agree with Grzenio and would add that the best way to handle a validation error down in the domain layer (aka business objects) is to generate an exception. That exception could propagate all the way up into the UI layer where it could be handled and interactively rectified with the user. However, depending on the capabilities and technologies involved, this may not always be feasible, in which case, you probably should be validating up in the UI layer (possibly in addition to the domain layer). It's less than ideal, but might be your only viable option. In any case, setting it to a default value is a horrible thing to do and will lead to subtle bugs that will be near impossible to diagnose. If done on a broad scale, you'll have an unmaintainable system in no time (especially if you have no unit tests backing you up).