Several people have asked me about using data annotations for validation outside of a UI framework, like ASP.NET MVC or Silverlight. The System.ComponentModel.DataAnnotations assembly contains everything you need to execute validation logic in the annotations. Specifically, there is a static Validator class to execute the validation rules. For example, let's say you have the following class in a console mode application:
public class Recipe
{
[Required]
public string Name { get; set; }
}
You could validate the recipe with the following code:
var recipe = new Recipe();
var context = new ValidationContext(recipe, serviceProvider: null, items: null);
var results = new List<ValidationResult>();
var isValid = Validator.TryValidateObject(recipe, context, results);
if (!isValid)
{
foreach (var validationResult in results)
{
Console.WriteLine(validationResult.ErrorMessage);
}
}
Result: "The Name field is required".
You can construct the ValidationContext class without a service provider or items collection, as shown in the above code, as they are optional for the built-in validation attributes. The Validator also executes any custom attributes you have defined, and for custom attributes you might find the serviceProvider useful as a service locator, while the items parameter is a dictionary of extra data to pass along. The Validator also works with self validating objects that implement IValidatableObject.
public class Recipe : IValidatableObject
{
[Required]
public string Name { get; set; }
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
// ...
}
}
Like everything framework related, the Validator tries to provide an API that will work in a number of validation scenarios. I recommend you bend it to your will and build something that makes it easy to use inside your specific design and architecture. A class like the following would be a step towards hiding some complexity.
public class DataAnnotationsValidator
{
public bool TryValidate(object @object, out ICollection<ValidationResult> results)
{
var context = new ValidationContext(@object, serviceProvider: null, items: null);
results = new List<ValidationResult>();
return Validator.TryValidateObject(
@object, context, results,
validateAllProperties: true
);
}
}