ProductAmount.cs

using System.Diagnostics.CodeAnalysis;
using MyCompany.ECommerce.TechnicalStuff;
using P3Model.Annotations.Domain.DDD;

namespace MyCompany.ECommerce.Sales.Products;

[DddValueObject]
public record ProductAmount(ProductId ProductId, Amount Amount)
{
    public ProductUnit ProductUnit => ProductUnit.Of(ProductId, Amount.Unit);

    public static ProductAmount Of(ProductId productId, int value, AmountUnit unit) =>
        new(productId, Amount.Of(value, unit));
        
    public static ProductAmount Of(ProductId productId, Amount amount) => new(productId, amount);
        
    [SuppressMessage("ReSharper", "UnusedMember.Local", Justification = "EF")]
    private ProductAmount() : this(default, default!) { }

    public static ProductAmount operator +(ProductAmount x, ProductAmount y)
    {
        CheckProductId(x, y);
        return Of(x.ProductId, x.Amount + y.Amount);
    }
        
    public static ProductAmount operator -(ProductAmount x, ProductAmount y)
    {
        CheckProductId(x, y);
        return Of(x.ProductId, x.Amount - y.Amount);
    }

    private static void CheckProductId(ProductAmount x, ProductAmount y)
    {
        if (!x.ProductId.Equals(y.ProductId)) throw new DomainError();
    }
}