不能使用’System.Data.Entity.Core.Objects.ObjectQuery类型的实例调用

我想通过userId查找用户名

这段代码片段正常工作

Discussion_CreateBy = db.AspNetUsers.Find(discussion.CreatedBy).UserName, 

这曾经不适用于以下控制器类

 Comment_CreateBy = db.AspNetUsers.Find(c.CreatedBy).UserName, 

这是我的模特课

 public class DiscussionVM { public int Disussion_ID { get; set; } public string Discussion_Title { get; set; } public string Discussion_Description { get; set; } public Nullable Discussion_CreateDate { get; set; } public string Discussion_CreateBy { get; set; } public string Comment_User { get; set; } public IEnumerable Comments { get; set; } } public class CommentVM { public int Comment_ID { get; set; } public Nullable Comment_CreateDate { get; set; } public string Comment_CreateBy { get; set; } public string Comment_Description { get; set; } } 

这是整个控制器类

  public ActionResult Discussion_Preview() { int Discussion_ID = 1; var discussion = db.AB_Discussion.Where(d => d.Discussion_ID == Discussion_ID).FirstOrDefault(); var comments = db.AB_DiscussionComments.Where(c => c.Discussion_ID == Discussion_ID); DiscussionVM model = new DiscussionVM() { Disussion_ID = discussion.Discussion_ID, Discussion_Title = discussion.Discussion_Name, Discussion_Description = discussion.Discussion_Name, Discussion_CreateBy = db.AspNetUsers.Find(discussion.CreatedBy).UserName, Discussion_CreateDate = discussion.CreatedDate, Comments = comments.Select(c => new CommentVM() { Comment_ID = c.Comment_ID, Comment_Description = c.Comment_Discription, Comment_CreateBy = db.AspNetUsers.Find(c.CreatedBy).UserName, Comment_CreateDate = c.CreatedDate }) }; return View(model); } 

获得以下错误

1[Project.Models.AspNetUser]' cannot be called with instance of type 'System.Data.Entity.Core.Objects.ObjectQuery在类型’System.Data.Entity.DbSet 1[Project.Models.AspNetUser]' cannot be called with instance of type 'System.Data.Entity.Core.Objects.ObjectQuery上声明的方法’Project.Models.AspNetUser Find（System.Object []）’ 1[Project.Models.AspNetUser]' cannot be called with instance of type 'System.Data.Entity.Core.Objects.ObjectQuery 1 [Project.Models.AspNetUser]’

Answer 1

 Discussion_CreateBy = db.AspNetUsers.Find(discussion.CreatedBy).UserName 

之所以有效是因为讨论是内存中的对象，因为您通过调用FirstOrDefault来执行查询：

 var discussion = db.AB_Discussion.Where(d => d.Discussion_ID == Discussion_ID).FirstOrDefault(); 

另一方面，在以下声明中：

db.AspNetUsers.Find(c.CreatedBy).UserName

c尚未被查询，因为

 db.AB_DiscussionComments.Where(c => c.Discussion_ID == Discussion_ID) 

返回IQueriable而不是实际的注释集合

解决它的最简单方法是将所有注释带入内存（因为你无论如何都需要它们）：

 var comments = db.AB_DiscussionComments.Where(c => c.Discussion_ID == Discussion_ID).ToList();