ValidationAspects

Features

• Object Validation - Objects can be queried to determine if their state is valid against a set of validation rules. Validation messages and context of what/where validation failed is reported via a ValidationResult. An object can also be validated as a method pre-condition by registering an object validator against the method.
• Property Validation - Multi-Mode validation. The following modes can be enabled or disabled independantly to suit your chosen method of validation:

1. Interception Validation - Validation is invoked when the property is set. If the validation fails, a validation exception will throw to ensure the model does not become invalid.
2. State Validation - Validation is invoked when the object is validated. If the validation fails, the validation failure is added to the ValidationResult.

• Parameter Validation - Parameter validation checks the validity of the value as determined by code contracts and business rules. If the validation fails, a validation exception will throw to ensure the model does not become invalid.
• Real-time augmentation / replacement - Validation can be changed programmatically or via Xaml configuration.
• AOP - Interception validation aspects are applied to your models by PostSharp or Unity. There are no base classes to derive from or interfaces to explicitly implement.
• Custom Validators - Implement new validators easily with minimal code with lambda syntax.
• Strongly-typed validation targets - Compile-time checking (PostSharp only) ensures validation is correctly declared - you can't declare a numeric validator to validate a string. Validators are implemented to target certain types. Incorrectly declared validators applied at run-time fail fast.
• Integration - Support for WPF, asp.net / asp.net MVC (via http://www.codeplex.com/xval), and Silverlight (State Validation only, PostSharp 1.5 interception in progress).
• Localization - Validation exception messages can be customized with message formatting functions.
• TDD'd - Near 100% code coverage from hundreds of unit tests.

Documentation

• FAQ
• List of the current Built-in Validators
• How to Declare Validation using Attributes
• How to write Custom Validators
• How to Programmatically Augment and Replace Validation at runtime
• How to set the Property Validation Modes
• How to handle Validation Exceptions
• How to Localize/Customize exception messages with Exception Formatting
• How to augment and replace validation with Xaml Configuration
• How to integrate with WPF
• How to integrate with asp.net MVC

Blog

Examples

[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");
  }
}

// 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()} );

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

try
{
  customer.Name = "";
}
catch (ValidationException e)
{
  foreach (string message in e.Messages) { ... }
}

Road Map

• Silverlight interception validation using PostSharp 1.5
• Quick Start examples.