Validation of Guid

Question

I have a strongly-typed view which has a DropDownListFor attribute on it.

Each item in the dropdown list is represented by a GUID.

What I\'m after is a way

Answer 1

If the custom validation doesn't require a high reuse in your system (i.e. without the need for a custom validation attribute), there's another way to add custom validation to a ViewModel / Posted data model, viz by using IValidatableObject.

Each error can be bound to one or more model properties, so this approach still works with e.g. Unobtrusive validation in MVC Razor.

Here's how to check a Guid for default (C# 7.1):

public class MyModel : IValidatableObject // Implement IValidatableObject
{
    [Required]
    public string Name {get; set;}
    public Guid SomeGuid {get; set;}
    ... other properties here

    public IEnumerable Validate(ValidationContext validationContext)
    {
        if (SomeGuid == default)
        {
            yield return new ValidationResult(
                "SomeGuid must be provided",
                new[] { nameof(SomeGuid) });
        }
    }
 }

More on IValidatableObject here