Edit

Use enumeration classes instead of enum types

  • Article

Tip

This content is an excerpt from the eBook, .NET Microservices Architecture for Containerized .NET Applications, available on .NET Docs or as a free downloadable PDF that can be read offline.

Download PDF

.NET Microservices Architecture for Containerized .NET Applications eBook cover thumbnail.

Enumerations (or enum types 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 sizes (small, medium, large) is a good example. Using enums for control flow or more robust abstractions can be a code smell. This type of usage leads 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 isn't a critical topic and in many cases, for simplicity, you can still use regular enum types if that's your preference. The use of enumeration classes is more related to business-related concepts.

Implement an Enumeration base class

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(int id, string name) => (Id, Name) = (id, name);

    public override string ToString() => Name;

    public static IEnumerable<T> GetAll<T>() where T : Enumeration =>
        typeof(T).GetFields(BindingFlags.Public |
                            BindingFlags.Static |
                            BindingFlags.DeclaredOnly)
                 .Select(f => f.GetValue(null))
                 .Cast<T>();

    public override bool Equals(object obj)
    {
        if (obj is not Enumeration otherValue)
        {
            return false;
        }

        var typeMatches = GetType().Equals(obj.GetType());
        var valueMatches = Id.Equals(otherValue.Id);

        return typeMatches && valueMatches;
    }

    public int CompareTo(object other) => 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(1, nameof(Amex));
    public static CardType Visa = new(2, nameof(Visa));
    public static CardType MasterCard = new(3, nameof(MasterCard));

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

Additional resources

Previous Next