How do I validate a property from a different class with DataAnnotations

I have a competition class and a competitionEntry class. A competition can have 5 questions (just string values) and the competitionEnt开发者_如何学JAVAry can have 5 answers (also only string values).

How would I validate that if a question is present that the answer should be present as well?

I think I need a custom validation attribute but how would I get the competition class properties to check if the answer is filled in and so the questions must also be?

I don't think you can do this with an attribute. It makes more sense to have the Competition class validate entries.

public class Competition
{
    public bool AnswersAreCorrectFor(CompetitionEntry entry)
    {
        // check answers
    }
    // ...
}

I haven't done this but AFAIK, you can definitely do it with DataAnnotations.

You can implement a subclass of ValidationAttribute.

Check out this question to get the idea.