DI-Enabled validation rules

UniqueUsernameRule.cs

public class UniqueUsernameRule : IFieldValidationRule
{
	private readonly IEntityRepository _repository;

	public UniqueUsernameRule(IEntityRepository repository)
	{
		_repository = repository;
	}

	public void Validate(Accessor accessor, ValidationContext context)
	{
		var email = accessor.GetValue(context.Target) as EmailAddress;
		if (email == null) return;

		var isUnique = !_repository.All<User>().Any(x => x.Username.Equals(email.Address, StringComparison.OrdinalIgnoreCase));
		if(!isUnique)
		{
			context.Notification.RegisterMessage(accessor, SurgeryLogisticsValidationKeys.USERNAME_IN_USE);
		}
	}
}

UniqueUsernameRuleSource.cs

public class UniqueUsernameRuleSource : IFieldValidationSource
{
	private readonly IEntityRepository _repository;

	public UniqueUsernameRuleSource(IEntityRepository repository)
	{
		_repository = repository;
	}

	public IEnumerable<IFieldValidationRule> RulesFor(PropertyInfo property)
	{
		var accessor = ReflectionHelper.GetAccessor<RegistrationRequest>(x => x.Email);
		var prop = new SingleProperty(property);

		if(accessor.Equals(prop))
		{
			yield return new UniqueUsernameRule(_repository);
		}
	}

	public void Validate()
	{
		// no-op
	}
}

ValidationStructureMapRegistry.cs

public class ValidationStructureMapRegistry : Registry
{
	public ValidationStructureMapRegistry()
	{
		this.FubuValidation();

		// ...
            
		For<IFieldValidationSource>().Add<UniqueUsernameRuleSource>();

		// Or just do an assembly scan and add all of your sources
	}
}