c＃lambda表达式错误...此字典需要

Question

类型的模型项目

当我更改查询时出现错误。能否请你帮忙？

public ActionResult Index(int? id) 
    { 
     Models.MyProjectEntities entity = new Models.MyProjectEntities(); 

     // NORMAL QUERY, NO PROBLEM 
     //var Messages = entity.Message.Where(x => x.Active); 

     // JOINED QUERY, GENERATES ERROR 
     var Messages = entity.Message.Join(entity.Categories, 
          m => m.CategoriID, 
          k => k.CategoriID, 
          (m, k) => new { Message = m, Categories = k }) 
          .Where(x => x.Message.Active); 


     return View(Messages); 
    } 

这里是aspx文件第一行

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<IEnumerable<MyProject.Models.Message>>" %> 

以下是错误

The model item passed into the dictionary is of type 'System.Data.Objects.ObjectQuery`1[<>f__AnonymousType7`2[MyProject.Models.Message,MyProject.Models.Categories]]', but this dictionary requires a model item of type 'System.Collections.Generic.IEnumerable`1[MyProject.Models.Message]'. 

Answer 1

你的观点被声明为取一组Message秒。
你正试图给它传递一组匿名类型。

由于错误明确指出，它不适合。

相反，您应该创建一个类来保存联接中的数据，然后将视图声明为获取该类的集合。
（查看不能轻易使用匿名类型机型）

Answer 2

因为你加入一个你创建一个匿名类型，你需要做的

var Messages = entity.Message.Join(entity.Categories, 
    m => m.CategoriID, 
    k => k.CategoriID, 
    (m, k) => new { Message = m, Categories = k }) 
    .Where(x => x.Message.Active) 
    .Select(x => new Message { ... .. .. }); 

Answer 3

public ActionResult Index(int? id) 
{ 
    Models.MyProjectEntities entity = new Models.MyProjectEntities(); 

    // NORMAL QUERY, NO PROBLEM 
    //var Messages = entity.Message.Where(x => x.Active); 

    // JOINED QUERY, GENERATES ERROR 
    var Messages = entity.Message.Join(entity.Categories, 
         m => m.CategoriID, 
         k => k.CategoriID, 
         (m, k) => new { Message = m, Categories = k }) 
         .Where(x => x.Message.Active) 
         .Select(x => x.Message); 


    return View(Messages); 
} 

，或者如果你需要的类别为好，你应该改变视图模型类型

编辑：

public ActionResult Index(int? id) 
{ 
    Models.MyProjectEntities entity = new Models.MyProjectEntities(); 

    // NORMAL QUERY, NO PROBLEM 
    //var Messages = entity.Message.Where(x => x.Active); 

    // JOINED QUERY, GENERATES ERROR 
    var Messages = entity.Message.Join(entity.Categories, 
         m => m.CategoriID, 
         k => k.CategoriID, 
         (m, k) => new MessageWithCategories { Message = m, Categories = k }) 
         .Where(x => x.Message.Active); 


    return View(Messages); 
} 

和模型类型应该是MessageWithCategories（这个类必须被创建）