Entity : An Entity unchanged over time could be a Value Object

Medium

---

DDD

If your entity doesn't change over time, it could be a Value Object.

If a class annotated with Entity has fields that are not readonly but never written or updated (except in constructors), then the practice is not followed and the class should be a Value Object, and fields marked as readonly.

Examples

Example 1:

Positive

Correct implementation following the practice.

namespace CurrencyConverter.Domain
{
    [ValueObject]
    public class Currency
    {
        private readonly string _name;

        public Currency(string name)
        {
            _name = name;
        }

        public override bool Equals(object obj)
        {
            return obj is Currency currency
                   && _name.Equals(currency._name);
        }

        public override int GetHashCode()
        {
            return (_name != null ? _name.GetHashCode() : 0);
        }

        public bool Is(string currencyName)
        {
            return _name.Equals(currencyName);
        }

    }
}

Negative

Incorrect implementation that violates the practice.

namespace CurrencyConverter.Domain
{
    [Entity]
    public class Currency
    {
        private string _name;

        public Currency(string name)
        {
            _name = name;
        }

        public string Name => _name;


        public bool Is(string currencyName)
        {
            return Name.Equals(currencyName);
        }
    }
}