CSLA.NET framework from Lhotka contains a lot of mechanisms for adding validations and business rules. Through CSLA.NET you can easily provide your own custom rules. Enterprise Library v3.0 now also contains a validation application block (VAB) that can be used through attributes and even from a configuration file.

The two validation mechanisms of validation are complementary. This can be done by adding a custom rule that uses the ValidationFactory of the VAB. This means we have something like:

public class VABRules
{
    public class VABRuleArgs : RuleArgs
    {
        private string _ruleset;

        public string Ruleset
        {
            get { return _ruleset; }
        }


        public VABRuleArgs(string propertyName) : this(propertyName, null)
        {
        }

        public VABRuleArgs(string propertyName, string ruleset) : base(propertyName)
        {
            _ruleset = ruleset;
        }
    }

    public static bool VABValid<T>(object target, RuleArgs e)
    {
        Validator<T> validator = ValidationFactory.CreateValidator<T>(((VABRuleArgs)e).Ruleset);

        if (validator == null)
            return true;

        ValidationResults results = validator.Validate(target);

        if (results == null)
            return true;

        foreach (ValidationResult result in results)
        {
            if (result.Key == e.PropertyName)
            {
                e.Description = result.Message;
                return false;
            }
        }

        return true;
    }
}

Having the VAB rule we simply need to decorate our properties with the validation attributes of VAB and an override of the AddBusinessRules method is needed to take into account the VAB rules. For example we can define a customer business object as follow:

[Serializable()]
public class Customer : Csla.BusinessBase<Customer>
{
    private int _id = 0;
    private string _firstName = string.Empty;
    private string _email = string.Empty;
    private int _rewardPoints;
    private string _countryCode = string.Empty;

    [Browsable(false), System.ComponentModel.DataObjectField(true, true)]
    public int Id
    {
        get
        {
            CanReadProperty("Id", true);
            return _id;
        }
    }

    [NotNullValidator(MessageTemplate="First Name may not be empty")]
    [StringLengthValidator(1, 60, MessageTemplate = "First Name must be between 1 and 60 characters long")]
    public string FirstName
    {
        get
        {
            CanReadProperty("FirstName", true);
            return _firstName;
        }
        set
        {
            CanWriteProperty("FirstName", true);
            if (!_firstName.Equals(value))
            {
                _firstName = value;
                PropertyHasChanged("FirstName");
            }
        }
    }

    [RegexValidator(@"\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*")]
    public string Email
    {
        get
        {
            CanReadProperty("Email", true);
            return _email;
        }
        set
        {
            CanWriteProperty("Email", true);
            if (!_email.Equals(value))
            {
                _email = value;
                PropertyHasChanged("Email");
            }
        }
    }

    [Int32RangeValidator(0, 1000000, MessageTemplate = "Rewards points cannot exceed 1,000,000")]
    public int RewardPoints
    {
        get
        {
            CanReadProperty("RewardPoints", true);
            return _rewardPoints;
        }
        set
        {
            CanWriteProperty("RewardPoints", true);
            if (!_rewardPoints.Equals(value))
            {
                _rewardPoints = value;
                PropertyHasChanged("RewardPoints");
            }
        }
    }

    [NotNullValidator(MessageTemplate = "Country may not be empty")]
    public string CountryCode
    {
        get
        {
            CanReadProperty("CountryCode", true);
            return _countryCode;
        }
        set
        {
            CanWriteProperty("CountryCode", true);
            if (!_countryCode.Equals(value))
            {
                _countryCode = value;
                PropertyHasChanged("CountryCode");
            }
        }
    }

    protected override object GetIdValue()
    {
        return _id;
    }

    protected override void AddBusinessRules()
    {
        ValidationRules.AddRule(VABRules.VABValid<Customer>, new VABRules.VABRuleArgs("FirstName"));
        ValidationRules.AddRule(VABRules.VABValid<Customer>, new VABRules.VABRuleArgs("Email"));
        ValidationRules.AddRule(VABRules.VABValid<Customer>, new VABRules.VABRuleArgs("RewardPoints"));
        ValidationRules.AddRule(VABRules.VABValid<Customer>, new VABRules.VABRuleArgs("CountryCode"));
    }
}