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Using Enumeration classes instead of enum types
.NET Microservices Architecture for Containerized .NET Applications | Using Enumeration classes instead of enum types
Docker, Microservices, ASP.NET, Container
CESARDELATORRE
wiwagn
05/26/2017
.net-core
dotnet-docker
article

Using Enumeration classes instead of enum types

Enumerations (enums for short) are a thin language wrapper around an integral type. You might want to limit their use to when you are storing one value from a closed set of values. Classification based on gender (for example, male, female, unknown), or sizes (S, M, L, XL) are good examples. Using enums for control flow or more robust abstractions can be a code smell. This type of usage will lead to fragile code with many control flow statements checking values of the enum.

Instead, you can create Enumeration classes that enable all the rich features of an object-oriented language. However, this is not a critical issue and in many cases, for simplicity, you can still use regular enums if that is your preference.

Implementing Enumeration classes

The ordering microservice in eShopOnContainers provides a sample Enumeration base class implementation, as shown in the following example:

public abstract class Enumeration : IComparable
{
    public string Name { get; private set; }
    public int Id { get; private set; }

    protected Enumeration()
    {
    }

    protected Enumeration(int id, string name)
    {
        Id = id;
        Name = name;
    }

    public override string ToString()
    {
        return Name;
    }

    public static IEnumerable<T> GetAll<T>() where T : Enumeration, new()
    {
        var type = typeof(T);
        var fields = type.GetTypeInfo().GetFields(BindingFlags.Public |
            BindingFlags.Static |
            BindingFlags.DeclaredOnly);
        foreach (var info in fields)
        {
            var instance = new T();
            var locatedValue = info.GetValue(instance) as T;
            if (locatedValue != null)
            {
                yield return locatedValue;
            }
        }
    }

    public override bool Equals(object obj)
    {
        var otherValue = obj as Enumeration;
        if (otherValue == null)
        {
            return false;
        }
        var typeMatches = GetType().Equals(obj.GetType());
        var valueMatches = Id.Equals(otherValue.Id);
        return typeMatches && valueMatches;
    }

    public int CompareTo(object other)
    {
        return Id.CompareTo(((Enumeration)other).Id);
    }

    // Other utility methods ...
}

You can use this class as a type in any entity or value object, as for the following CardType Enumeration class.

public class CardType : Enumeration
{
    public static CardType Amex = new CardType(1, "Amex");
    public static CardType Visa = new CardType(2, "Visa");
    public static CardType MasterCard = new CardType(3, "MasterCard");

    protected CardType() { }

    public CardType(int id, string name)
        : base(id, name)
    {
    }


    public static IEnumerable<CardType> List()
    {
        return new[] { Amex, Visa, MasterCard };
    }
    // Other util methods
}

Additional resources

[!div class="step-by-step"] [Previous] (implement-value-objects.md) [Next] (domain-model-layer-validations.md)