实体框架错误：“导航属性只能参与单个关系”

Question

我的设置类似于下面

public class Component
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Type { get; set; }
    public List<ComponentUpdate> Updates { get; set; }
    public ComponentUpdate LastUpdate { get; set; }
}

public class ComponentUpdate
{
    public int Id { get; set; }
    public DateTime Timestamp { get; set; }
    public Component Component { get; set; }
    public string Message { get; set; }
}

我已经设置好了

modelBuilder.Entity<Component>().HasMany(c => c.Updates).WithOne(u => u.Component);
modelBuilder.Entity<ComponentUpdate>().HasOne(u => u.Component).WithOne(c => c.LastUpdate);

但 Entity Framework 抛出错误：

导航属性只能参与单个关系

以上设置有什么问题？我有时想使用导航属性获取最后更新。这似乎是一个 EF 限制...

Answer 1

您必须为每个关系定义一个单独的导航属性，并且还必须为第二个关系定义一个外键：

   public class Component
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Type { get; set; }
        public List<ComponentUpdate> Updates { get; set; }
        public ComponentUpdate LastUpdate { get; set; }
    }


    public class ComponentUpdate
    {
        public int Id { get; set; }
        public DateTime Timestamp { get; set; }
        public Component Component { get; set; }
        public int SecondComponentId { get; set; }
        public Component SecondComponent { get; set; }
        public string Message { get; set; }
    }
    
     builder.Entity<Component>()
        .HasMany(c => c.Updates)
        .WithOne(u => u.Component);

     builder.Entity<ComponentUpdate>()
        .HasOne(u => u.SecondComponent)
        .WithOne(c => c.LastUpdate)
        .HasForeignKey<ComponentUpdate>(x => x.SecondComponentId);