Enum conversion to Enumeration class with small Business Logic inside

Question

I had old enum, I converted it to Enumeration class and added one method inside (isValid). I am not sure if it is good approach to add such small business logic into Enumeration class. I would like to understand if this is a good approach or not.

Here is old enum:

internal enum Rule
{
 None = 0,
 CompensationIsZero = 1,
 CompensationLessThanDemand = 2,
 CompensationBetweenZeroAndDemand = 3,
 CompensationEqualsDemand = 4,
 CompensationLessOrEqualsDemand = 5
}

Here it is rewritten to Enumeration class and IsValid method is added.

 public class Rule : Enumeration
{
 public static readonly Rule None = new Rule (0, "None");
 public static readonly Rule CompensationIsZero = new Rule (1, "CompensationIsZero ");
 public static readonly Rule CompensationLessThanDemand = new Rule(2, "CompensationLessThanDemand "); 
 .... 
 // there are about 5 rules
 public Rule(int id, string name)
 : base(id, name)
 { }
 public bool IsValid(decimal compensation, decimal demand, int rule) {
 if (rule == Rule.None.Id) return true;
 if (rule == Rule.CompensationIsZero.Id) then return compensation == 0;
 if (rule == Rule.CompensationLessThanDemand .Id) then return compensation < demand;
 ...
 }
}

Enumeration class implementation version is very similar like in this article (https://docs.microsoft.com/en-us/dotnet/architecture/microservices/microservice-ddd-cqrs-patterns/enumeration-classes-over-enum-types)

Thus I have values compensation and demand (these come from UI). And I have some type based on which I get Rule value from database. And so I call method IsValid (compensation, demand, ruleIdFromDb). If it is not validated then I show error on UI.

Answer 1

Shouldn't the 'IsValid' method be static? I suppose you use it like Rule.IsValid(calculatedCompensation, 0, Rule.CompensationIsZero.Id), (as general idea, obviously it can be simplified).

Anyway PERSONALLY I would not do this, because Rule is no more an Enum, you gave it logic, that usually Enum don't have. I would have keep the Enum as original and built on top of that a Class with the required logic. (Maybe called RuleValidator with a static method public static bool IsValid(Rule rule, decimal compensation, decimal demand) {...}.

If this does not concern you, than another way could be to write an extension method:

static class RuleExtensions 
{
 public static bool Validate(this Rule rule, decimal compensation, decimal demand) 
 {
 switch (rule) 
 {
 case None: return true;
 case CompensationIsZero: return compensation == 0;
 case CompensationLessThanDemand : return compensation < demand;
 // ecc...
 }
 }
}

• renathy: Your comment make sense.
• renathy: can I ask one more question, what if I would like to have different error messages based on which Case failed. Should I add static property ErrorMessage or should error message be returned from Validate?
• Federico Rossi: I can't think a super elegant solution, I'm still junior. But I would go for something like public static bool Validate (this Rule rule, decimal compensation, decimal demand, out string errorMessage) {...}. Usage: if (!Rule.None.Validate.(10, 0, out var error)) Console.WriteLine(error);. Inside Validate then, before returning false, you would set errorMessage with a string retrieved form some kind of external resource (like the .resx files, or a DB). This because you could need the message to change (like for localization).