ValidationAspects

ValidationAspects looks to be a very nice library. Wery well tested with ~100% test coverage and wrapped with PostSharp (as a separate dll).
I've checked it into lib/ - use it on all Entities to set validations.

[Validate]
public class Customer
{
  private string _email;

  // apply validation to property setters
  [NotNullOrEmpty] public string Name { get; set; }
  [Minimum(0)] public int Age { get; set; }

  // apply validation to method parameters
  public void SetEmail([NotNullOrEmpty] string email) { _email = email; }

  // provide validation for objects either with methods or declaring validators on the class
  [ValidationMethod]
  public static void ValidateEmail(Customer customer)
  {
    if (string.IsNullOrEmpty(customer._email))
      throw new ValidationException("Email is not valid");
  }
}

Programmatic Registration:

// register lambda syntax validation functions
typeof(User).GetProperty("Name").AddValidation<string>((name, context) => { if (!Exists(name)) { throw new ValidationException("Username is unknown"); } } );

// register validation factories (classes)
typeof(User).GetProperty("Name").AddValidation(new [] { new NotNullOrEmpty()} );

// don't like strings?
TypeOf<User>.Property(user => user.Name).AddValidation(new [] { new NotNullOrEmpty()} );

Object Validation:

ValidationResult result = customer.Validate();
if (!result.IsValid)
{
  foreach (string message in result.Messages) { ... }
}

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ValidationAspects