How do I use IValidatableObject?

Question

I understand that IValidatableObject is used to validate an object in a way that lets one compare properties against each other.

I\'d still like to have

Answer 1

Just to add a couple of points:

Because the Validate() method signature returns IEnumerable<>, that yield return can be used to lazily generate the results - this is beneficial if some of the validation checks are IO or CPU intensive.

public IEnumerable Validate(ValidationContext validationContext)
{
    if (this.Enable)
    {
        // ...
        if (this.Prop1 > this.Prop2)
        {
            yield return new ValidationResult("Prop1 must be larger than Prop2");
        }

Also, if you are using MVC ModelState, you can convert the validation result failures to ModelState entries as follows (this might be useful if you are doing the validation in a custom model binder):

var resultsGroupedByMembers = validationResults
    .SelectMany(vr => vr.MemberNames
                        .Select(mn => new { MemberName = mn ?? "", 
                                            Error = vr.ErrorMessage }))
    .GroupBy(x => x.MemberName);

foreach (var member in resultsGroupedByMembers)
{
    ModelState.AddModelError(
        member.Key,
        string.Join(". ", member.Select(m => m.Error)));
}