EF核心值对象

Question

我使用一个value对象来表示Price

public record Price(decimal Amount, string Currency);

那么我有两个价格

的实体

public class Item 
{
public Price { get; private set; }
// rest of properties
}
public class OrderPosition 
{
public Price { get; private set; }
// rest
}

在DB中，我希望有这两个表

Items
| Id | Price_Amount | Price_Currency |

OrderPositions
| Id | Price_Amount | Price_Currency |

为了实现这一点，我将价格配置为商品的拥有类型以及订单位置:

public class ItemConfiguration : IEntityTypeConfiguration<Item>
{
public void Configure(EntityTypeBuilder<Item> builder)
{
builder.OwnsOne(i => i.Price);
}
}
public class ItemConfiguration : IEntityTypeConfiguration<OrderPosition>
{
public void Configure(EntityTypeBuilder<OrderPosition> builder)
{
builder.OwnsOne(op => op.Price);
}
}

这一切都很好，但是当我在一个项目上有相同的价格以及订单位置时，EF会给我一个警告:

[09:47:59 WRN] The same entity is being tracked as different entity types 'Item.Price#Price' and 'OrderPosition.Price#Price' with defining navigations. If a property value changes, it will result in two store changes, which might not be the desired outcome.

我完全理解这个异常，它甚至被记录为一个设计限制:https://learn.microsoft.com/en-us/ef/core/modeling/owned-entities#by-design-restrictions

Instances of owned entity types cannot be shared by multiple owners (this is a well-known scenario for value objects that cannot be implemented using owned entity types).

但是你怎么解决这个问题呢?我是否需要为ItemPrice和OrderPositionPrice创建一个派生类，并相互进行隐式转换?这是可行的，但我认为这不是最好的解决方案。

Answer 1

对于上述EF Core约束，重要的是不要传递相同的值，而是传递一个副本。。

public record Price(decimal Amount, string Currency)
{
public Price Copy() => new(this);
}
// used
var price = new Price(42.0, "USD");
item.Price = price.Copy();
orderPosition.Price = price.Copy();