Either or has to have a value but both can't be null at the same time

Question

I have two fields and I need to generate an attribute, using Microsoft Enterprise Library validation, so that either or has to have a value, but both can not be null at the same time.

Answer 1

Use a custom validator.

[HasSelfValidation]
public class ValidateMe {


    [SelfValidation]
    public void ValidateFieldNotNul(ValidationResults validationResults)
    {
       .. start psudo code
         if( xor)
             validationResults.AddResult( new ValidationResult("One must not be null",...));
    }

}

Answer 2

The Validation Application Block has a PropertyComparisonValidator which will let you compare one property with another. Unfortunately, this validator only allows a ComparisonType of: Equal, NotEqual, GreaterThan, GreaterThanEqual, LessThan, LessThanEqual so this doesn't actually help you.

I think you have 2 options:

• Self Validation
• Custom Validator

Self Validation (shown by @Nix) is probably the easiest but would require this to be reimplemented for every scenario where you have that requirement (at least to put the hooks to call a common method).

Creating a custom validator would result in code that could be added to the configuration or attributed directly on entities and that could easily be reused.

A custom validator will definitely be more work but may be worth it if you need the reuse (it can be reused across applications, for example) or prefer that design.