Value Object : All fields should be final/read-only

Medium

---

DDD

Value Objects are classes annotated with [ValueObject].

If your fields are not read-only and you update the fields, maybe it's an entity.

If your fields are not read-only and you don't update the fields, your fields have to be read-only.

Violations are raised on class fields that are not readonly but are never written, excepting in Constructors.

Examples

Example 1:

Negative

Incorrect implementation that violates the practice.

namespace Practices.DDD.ValueObject.AllReadOnly
{
    [ValueObject]
    public class ValueObject
    {
        private int _someProperty;
        private readonly int _anotherProperty;

        public ValueObject(int someProperty, int anotherProperty)
        {
            _someProperty = someProperty;
            _anotherProperty = anotherProperty;
        }

        
        public int SomeProperty
        {
            get => _someProperty;
            set => _someProperty = value;
        }
        
        public int AnotherProperty => _anotherProperty;
    }
}

Example 2:

Positive

Correct implementation following the practice.

namespace Practices.DDD.ValueObject.AllReadOnly
{
    [ValueObject]
    public class ValueObject
    {
        private readonly int _someProperty;
        private readonly int _anotherProperty;

        public ValueObject(int someProperty, int anotherProperty)
        {
            _someProperty = someProperty;
            _anotherProperty = anotherProperty;
        }

        public int SomeProperty => _someProperty;
        public int AnotherProperty => _anotherProperty;
    }
}

Negative

Incorrect implementation that violates the practice.

namespace Practices.DDD.ValueObject.AllReadOnly
{
    [ValueObject]
    public class ValueObject
    {
        private int _someProperty;
        private readonly int _anotherProperty;

        public ValueObject(int someProperty, int anotherProperty)
        {
            _someProperty = someProperty;
            _anotherProperty = anotherProperty;
        }

        public int SomeProperty => _someProperty;
        public int AnotherProperty => _anotherProperty;
    }
}