Question

我的项目中有用户模型和事件模型。事件具有创建者（用户）并具有参与者（用户），因此事件与用户具有一对多关系，并且与同一个表具有多对多关系。

我首先是这样的一对多关系：

Public class Event
{
      ...
      public int CreatedById { get; set; }
      public virtual User CreatedBy { get; set; }
      ...
}

然后当我添加多对多关系时，迁移不会产生多对多的关系：

Public class User
{
      ...
      public virtual ICollection<Event> Events { get; set; }
      ...
}

Public class Event
{
      ...
      public int CreatedById { get; set; }
      public virtual User CreatedBy { get; set; }
      public virtual ICollection<User> Users { get; set; }
      ...
}

如果我删除了一对多关系，那么迁移会成功生成多对多关系。

有没有办法只用数据注释来做到这一点？

Answer 1

EF不知道User.Events必须映射到哪里。它可以是Event.CreatedBy，也可以是Event.Users。两者都会产生有效的模型。您必须通过应用[InverseProperty]属性

给EF一点提示

public class User
{
    ...
    [InverseProperty("Users")]
    public virtual ICollection<Event> Events { get; set; }
    ...
}

Answer 2

使用Code First Approach，我总是建议使用流畅的API而不是使用DataAnnotations，它会自动使用一些转换。

这样，您就会知道自己的确切配置。

如果我是你，这就是我要用的：

public class EventMap : EntityTypeConfiguration<Event>
{
    public EventMap()
    {
        this.HasRequired(m => m.CreatedBy) // envent must have a creator
            .WithMany() // a user can have 0,1 or more events created by him
            .HasForeignKey(m => m.CreatedById) // specify property to be used as FK
            .WillCascadeOnDelete(true); // delete all events created by user if that specific user is deleted

        this.HasMany(m=>m.Users) // an event can have 0,1 or more participants
            .WithMany(m=>m.Events) // a user can be a participant in 0,1 or more events                
            .Map(m => m.MapLeftKey("EventId").MapRightKey("UserId")); // this will generate intermediate table to hold participant information - dbo.EventUser with EventId & UserId
            // Cascade Delete is always true for Many to Many mapping. however, it doesn't delete entry in other table, it deletes entry in Joined Table only.
    }
}

实体框架代码优先：与同一个表的一对多和多对多关系

2 个答案: