What are the benefits of using Data Annotation over a service layer in ASP.NET validation?

I'm looking at adding validation into my web app. Some models' validity depends on the state of other models in the app.

What are the开发者_如何学Python benefits of using the data annotation framework over a service layer? It seems to me that the service implementation would be easier, however I understand the benefits of having validation close to the data.

Thanks!

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MVC 3 / MVC 2 with .NET 4.0

Sounds like you want to use IValidatableObject, Scott Gu wrote a blog post about this.

What I normaly do if I have an Entity Framework model and I want to add custom validation to my object I do a partial class like this:

public partial class MyObjectModel : IValidatableObject
{
    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (someNumberProperty > anotherNumberProperty) 
            yield return new ValidationResult(
                    "someNumber property is larger than anotherNumberProperty", 
                                              new[] { "someNumberProperty" });
        if (someNumberProperty == 0) 
            yield return new ValidationResult("someNumber property cannot be 0", 
                                                new[] { "someNumberProperty" });

    }
}

MVC 2

Here is a another post by Scott Gu on how to acheive model validation but you might want to look in to Custom Validation.