Entity validation with different scenario - asp.net-mvc

Question

On the assumption that I have Entity with couple of fields. Some fields are required at some specific state but others only on further/other state.
public class Entity
{
//Required always
public SomeReference {}
//Required in specific situation/scenario
public OtherReference {}
}
How to achieve that scenario with some known validation framework or how to do it by my self?
For help:
Udi Dahan has some thoughts on this.
http://www.udidahan.com/2007/04/30/generic-validation/

Answer 1

I have a solution that I am using at the moment. I use Fluent validation and am still getting used to it. I can give you an example of a simple scenario I have. maybe it helps. I have a user class, with a address Object property. At some point, I want to only validate the User details(name, email, password, etc) and at another state I want to validate the user address(first line, postcode, etc).
Classes look like this:
public class User {
public virtual string Name { get; set; }
public virtual string Email { get; set; }
public virtual string Password { get; set; }
public virtual Address Address { get; set; }
}
public class Address {
public virtual string Address1 { get; set; }
public virtual string PostCode { get; set; }
}
I then have two (simplfied) validators, one for an address and one for a user:
public AddressValidator() {
RuleFor(address => address.Address1)
.NotNull()
.WithMessage("Please enter the first line of your address");
RuleFor(address => address.PostCode)
.NotNull()
.WithMessage("Please enter your postcode")
.Matches(UK_POSTCODE_REGEX)
.WithMessage("Please enter a valid post code!");
}
public UserValidator() {
RuleFor(user => user.FirstName)
.NotNull()
.WithMessage("Please provide a first name")
.Length(3, 50)
.WithMessage("First name too short");
RuleFor(user=> user.Password)
.Length(8, 50)
.WithMessage("Password is too short");
}
I then create a Model Validator, so for example, say we have a form where the user enters an address, we create a AddressModelValidator, and can re-use the validators we have written:
public AddressModelValidator() {
RuleFor(user => user.id)
.NotNull()
.WithMessage("An error has occured, please go back and try again");
RuleFor(user => user.Address).SetValidator(new AddressValidator());
}
So, with some thought, you can really create some nice models, and reduce your validation code duplication!

Answer 2

My preferernce is to localize common validation functions such as email and date validations into a ValidationService class that I can pass my object into. For the rest though I tend to put the validation into the class itself. If I am using LINQ to SQL then I can create a Validate() method on my object which LINQ to SQL will call prior to saving the object to the db like this:
public void Validate()
{
if(!IsValid)
throw new ValidationException("Rule violations prevent saving");
}
public bool IsValid
{
get { return GetRuleViolations().Count() == 0;}
}
public IEnumerable<RuleViolation> GetRuleViolations()
{
if(this.TermID == 0)
yield return new RuleViolation(HelpMessageService.GetHelpMessageBodyByID(1), "agreeWithTerms");
if(ValidationService.ValidateDate(this.Birthdate.ToString()))
yield return new RuleViolation(HelpMessageService.GetHelpMessageBodyByID(2), "birthDate");
if (!(Username.Length >= ConfigurationService.GetMinimumUsernameLength()) ||
!(Username.Length <= ConfigurationService.GetMaximumUsernameLength()))
yield return new RuleViolation(HelpMessageService.GetHelpMessageBodyByID(5), "username");
if(ValidationService.ValidateUsernameComplexity(Username))
yield return new RuleViolation(HelpMessageService.GetHelpMessageBodyByID(6), "username");
if (AccountID == 0 && ObjectFactory.GetInstance<IAccountRepository>().UsernameExists(this.Username))
yield return new RuleViolation(HelpMessageService.GetHelpMessageBodyByID(7), "username");
if (!ValidationService.ValidateEmail(Email))
yield return new RuleViolation(HelpMessageService.GetHelpMessageBodyByID(8), "email");
if (AccountID == 0 && ObjectFactory.GetInstance<IAccountRepository>().EmailExists(this.Email))
yield return new RuleViolation(HelpMessageService.GetHelpMessageBodyByID(9), "email");
yield break;
}
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