Validation in C# with System.ComponentModel

Validation.cs

public interface IObjectValidator<T>
{
  IEnumerable<ValidationResult> Validate(T @object);
}

public bool Validate(T objeto, out ICollection<ValidationResult> results)
{
  var validationResults = new List<ValidationResult>();

  // Default validation
  var context = new ValidationContext(objeto, serviceProvider: null, items: null);
  bool selfValidationFailed = !Validator.TryValidateObject(objeto, context, validationResults, validateAllProperties: true);

  // Object validators
  var validators = ServiceLocator.Current.GetAllInstances<IObjectValidator<T>>();
  foreach (var validator in validators)
  {
    var validatorResults = validator.Validate(objeto);
    foreach (var item in validatorResults)
      validationResults.Add(item);
  }
  
  results = validationResults;
  return results.Count > 0;
}

public void Validate<T>(T item)
{
  ICollection<ValidationResult> results;
  if (!Validate(item, out results))
    throw new ValidationErrorsException(results);
}

public class SomeEntityValidation : IObjectValidator<SomeEntity>
{
  readonly ISomeRepository _repository;
  public SomeEntityValidation(ISomeRepository repository)
  {
      _repository = repository;
  }
  
  public IEnumerable<ValidationResult> Validate(SomeEntity entity)
  {
    // TODO: global validation rules here
  }
}

[Serializable]
public class ValidationErrorsException : Exception
{
    IEnumerable<ValidationResult> ValidationResults { get; set; }

    public ValidationErrorsException()
    {
    }

    public ValidationErrorsException(IEnumerable<ValidationResult> validationResults)
    {
        ValidationResults = validationResults;
    }

    public ValidationErrorsException(string message) : base(message)
    {
    }

    public ValidationErrorsException(string message, Exception innerException) : base(message, innerException)
    {
    }

    protected ValidationErrorsException(SerializationInfo info, StreamingContext context) : base(info, context)
    {
    }
}

// WebAPI exception handler
public class CustomExceptionHandler : ExceptionHandler
{
  public override void Handle(ExceptionHandlerContext context)
  {
    var exception = context.Exception as ValidationErrorsException;
    if (exception != null)
    {
      var modelState = new ModelStateDictionary();
      foreach (var validationResult in exception.ValidationResults)
      {
        foreach (var memberName in validationResult.MemberNames)
        {
          modelState.AddModelError(memberName, validationResult.ErrorMessage);
        }
      }

      context.Result = new InvalidModelStateResult(
        modelState,
        true,
        new DefaultContentNegotiator(),
        context.Request,
        new MediaTypeFormatter[] { new JsonMediaTypeFormatter() }
      );
    }
  }
}