c# - 将 EF 实体映射到维护 ICollection 和延迟加载的 ViewModel

Question

自从转移到 EF 6 以来，这一直困扰着我。我们现在如何将集合映射到 View 模型，以便使用 IEnumerables 映射回更改并不痛苦。下面是演示我的问题的代码片段:

实体 - SS.Entity.Event

[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
public virtual ICollection<SS.Entity.User> Broadcasters { get; set; }
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
public virtual ICollection<SS.Entity.User> Viewers { get; set; }

模型 - SS.Model.Event

public virtual ICollection<SS.Model.User> Broadcasters { get; set; }
public virtual ICollection<SS.Model.User> Viewers { get; set; }

集合修改后映射回实体

Broadcasters = e.Broadcasters.Select(u => new SS.Entity.User
{
    Id = u.Id,
    SkypeId = u.SkypeId,
    Name = u.Name
}).ToList(), // THIS IS THE PROBLEM
Viewers = e.Viewers.Select(u => new SS.Entity.User
{
    Id = u.Id,
    SkypeId = u.SkypeId,
    Name = u.Name
}).ToList() // THIS IS THE PROBLEM

问题是我无法将一个 ICollection 映射到另一个 ICollection，因为 Select 生成一个 IEnumerable，这使得之后将属性映射回 EF 很痛苦，因为我必须重新创建集合或枚举它以更新它。我知道我遗漏了一些明显的东西，我已将 ICollection 更新为虚拟的，如其他答案中所述，但我不清楚这有何帮助。

如有任何帮助，我们将不胜感激!

杰拉德

Answer 1

假设您的“.ToList()”问题是在保存回数据库时出现的，这是您要找的吗？:

 var event = new SS.Entity.Event {Name = "New Name" and other properties};

 IEnumerable<SS.Entity.User> broadcasters = e.Broadcasters
        .Select(u => new SS.Entity.User
             {
              Id = u.Id,
              SkypeId = u.SkypeId,
              Name = u.Name
           });

 var viewers = e.Viewers.Select(u =>
          new SS.Entity.User
          {
             Id = u.Id,
             SkypeId = u.SkypeId,
              Name = u.Name
          });

 //add broadcasters to event
 event.Broadcasters.AddRange(broadcasters);

 //add viewers to event
 event.Viewers.AddRange(viewers);

 dataContext.Events.Add(event);
 dataContext.SaveChanges();