C# 无法使用类型为'；System.Data.Entity.Core.Objects.ObjectQuery

我想按用户ID查找用户名

此代码段正在运行

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

这在下面的控制器类中不起作用

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

    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);
    }

这是我的模型课

public class DiscussionVM
{
    public int Disussion_ID { get; set; }
    public string Discussion_Title { get; set; }
    public string Discussion_Description { get; set; }
    public Nullable<System.DateTime> Discussion_CreateDate { get; set; }
    public string Discussion_CreateBy { get; set; }

    public string Comment_User { get; set; }

    public IEnumerable<CommentVM> Comments { get; set; }

}

public class CommentVM
{

    public int Comment_ID { get; set; }
    public Nullable<System.DateTime> Comment_CreateDate { get; set; }
    public string Comment_CreateBy { get; set; }
    public string Comment_Description { get; set; }

}

获取以下错误

无法使用类型为“System.Data.Entity.Core.Objects.ObjectQuery”的实例调用在类型为“System.Data.Entity.DbSet

1[Project.Models.AspNetUser]”上声明的方法“Project.Models.AspNetUser Find（System.Object[]）

之所以有效，是因为讨论是内存中的对象，因为您正在通过对其调用
FirstOrDefault
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
尚未查询，因为

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

返回一个
IQueriable
，而不是实际的注释集合

修复此问题的最简单方法是将您的所有注释都带到内存中（因为您无论如何都需要它们）：

正如您所说，我更改了代码段，那么对于代码段，我应该引用什么呢？它是否也会更改
Comment_CreateBy=db.AspNetUsers.Find（c.CreatedBy）.UserName
您需要做的唯一更改是：
var comments=db.AB_DiscussionComments.Where（c=>c.Discussion_ID==Discussion_ID）.ToList（）你真是天才
db.AB_DiscussionComments.Where(c => c.Discussion_ID == Discussion_ID)

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