当您有两个表需要一个第三个表作为参考，而第三个表不能单独存在时，如何建立关系模型，如下所示：

`User` has an `Address`
`Shop` has an `Address`
 An `Address` can either belong to a `Shop` or to a `User` , but it can't exist on its own.
 User and Shop must not be modelled as derived entities from a superclass (in code) since they got nothing in common

下面的方法是使用来自这两者的外键 User 以及 Shop 但是我不喜欢这种方法，因为我不想让所有使用 Address 内部 Address 有没有其他方法来保持 Address 班级 clean ?

public class Address
{   
   public long Id{get;set;}
   [ForeignKey(nameof(User)]
   public long? UserId{get;set;}
   [ForeignKey(nameof(Shop)]
   public long? ShopId{get;set;}
   public class User User {get;set;}
   public class Shop Shop {get;set;}

}

public class User
{
   public long Id{get;set;}
   [InverseProperty(nameof(Address.User)]
   public long AddressId {get;set;}
   public Address Address {get;set;}
}
public class Shop
{
   public long Id{get;set;}
   [ForeignKey(nameof(Address.Shop)]
   public long AddressId {get;set;}
   public Address Address {get;set;}
}

在fluent api中，它类似于：

modelBuilder.Entity<Address>().HasOne(y=>y.User).WithOne(z=>z.Address).OnDelete(Cascade);
modelBuilder.Entity<Address>().HasOne(y=>y.Shop).WithOne(z=>z.Address).OnDelete(Cascade);

永远不会有这样的情况 Address 两者都有 User 以及
Shop NOT NULL