不能使用类型为'System.Data.Entity.Core.Objects.ObjectQuery的实例进行调用 [英] cannot be called with instance of type 'System.Data.Entity.Core.Objects.ObjectQuery

问题描述

我想通过userId查找用户名

I want to Find Username by userId

此代码段有效

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

这曾经在以下控制器类中不起作用

and this once not working in following controller class

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

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; }

}

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);
    }

出现以下错误

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

Method 'Project.Models.AspNetUser Find(System.Object[])' declared on type 'System.Data.Entity.DbSet1[Project.Models.AspNetUser]' cannot be called with instance of type 'System.Data.Entity.Core.Objects.ObjectQuery1[Project.Models.AspNetUser]'

推荐答案

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

之所以行之有效，是因为讨论是一个内存对象，因为您正在通过在其上调用FirstOrDefault来执行查询:

Works because discussion is an in-memory object because you are executing a query by calling FirstOrDefault on it:

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

另一方面，以下语句:

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

c，因为

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

返回一个IQueriable而不是评论的实际集合

returns an IQueriable and not the actual collection of comments

最简单的解决方法是将所有注释都存储到内存中(因为无论如何您都需要它们):

The easiest way to fix it is to bring all your comments into memory (since you are anyway need them all) :

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

这篇关于不能使用类型为'System.Data.Entity.Core.Objects.ObjectQuery的实例进行调用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！