Question

Suppose you have a viewModel:

public class CreatePersonViewModel
{
    [Required]
    public bool HasDeliveryAddress {get;set;}

    // Should only be validated when HasDeliveryAddress is true
    [RequiredIf("HasDeliveryAddress", true)]
    public Address Address { get; set; }
}

And the model Address will look like this:

public class Address : IValidatableObject
{
    [Required]
    public string City { get; set; }
    [Required]        
    public string HouseNr { get; set; }
    [Required]
    public string CountryCode { get; set; }
    [Required]
    public string FirstName { get; set; }
    [Required]
    public string LastName { get; set; }
    [Required]
    public string ZipCode { get; set; }
    [Required]
    public string Street { get; set; }

    #region IValidatableObject Members

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        string[] requiredFields;
        var results = new List<ValidationResult>();

        // some custom validations here (I removed them to keep it simple)

        return results;
    }

    #endregion
}

Some would suggest to create a viewmodel for Address and add some custom logic there but I need an instance of Address to pass to my EditorTemplate for Address.

The main problem here is that the validation of Address is done before the validation of my PersonViewModel so I can’t prevent it.

Note: the RequiredIfAttribute is a custom attribute which does just what I want for simple types.

Answer 1

Would have been a piece of cake if you had used FluentValidation.NET instead of DataAnnotations or IValidatableObject which limit the validation power quite in complex scenarios:

public class CreatePersonViewModelValidator : AbstractValidator<CreatePersonViewModel>
{
    public CreatePersonViewModelValidator()
    {
        RuleFor(x => x.Address)
            .SetValidator(new AddressValidator())
            .When(x => x.HasDeliveryAddress);
    }
}