LINQ 存储库和方法 return

Question

我是 C#、MVC、LINQ、Entity Framework 以及我正在做的所有其他事情的新手。我已经在这个问题上选择了 Whosebug brain-trust 和其他网站，但看不到如何解决它。

我正在尝试为我们正在构建的新应用程序实现存储库模式，但在返回查询结果时遇到问题。第一个也是最紧迫的问题是我收到以下错误，第二个问题更多的是弄清楚如何处理查询中的空结果。

对于这个问题，我正在尝试从数据库中获取请求列表以显示在仪表板视图中。我们有一个使用 SQL 查询的工作原型，我正在尝试用存储库替换它，这可能有点过分，但这是我们想要做的事情。

视图如下：

@using RAM.DAL.Models
@model RequestViewModel
@{
    ViewBag.Title = "Dashboard";
} 

<h1>Dashboard</h1>

<div class="col-md-4">
    <h2>Resource Requests</h2>
        <div class="panel">
            <table class="table table-hover">
                <thead>
                    <tr class="bg-primary">
                        <th>Number</th>
                        <th>Mission Title</th>
                        <th>Resource Requested</th>
                        <th>Person</th>
                    </tr>
                </thead>
                <tbody>
                    @if (Model.isEmpty)
                    {
                        <tr>
                            <td colspan="4">No requests pending</td>
                        </tr>
                    }
                    else
                    {
                        <tr onclick="location.href= '@Url.Action("Assignment", "Mission", new { id = Model.ID })'">
                            <td>@Model.ID</td>
                            <td>@Model.title</td>
                            <td>@Model.resourceTitle</td>
                            <td>@Model.userName</td>
                        </tr>
                    }
                </tbody>
            </table>
    </div>
    <!--<p><a class="btn btn-default" href="#">Content 1 Btn &raquo;</a></p>-->
</div>

这是视图模型：

using System;

namespace RAM.DAL.Models
{
    public class RequestViewModel
    {
        public int? ID { get; set; }
        public string title { get; set; }
        public string requestText { get; set; }
        public string user_ID { get; set; } //The userID of the user being requested.
        public string userName { get; set; } //Full name of the user being requested
        public int? fromResourceID { get; set; } //The resource where the request was generated from
        public int? toResourceID { get; set; } //The resource where the reassigned worker is requested to go to
        public string resourceTitle { get; set; } //Title of the resource where the reassigned worker is requested to go to
        public DateTime? requestDate { get; set; }//The date the request was made
        public bool? isEmpty { get; set; }
    }
}

这是我遇到问题的 GetRequests 方法的存储库（其余尚未实现）：

using RAM.DAL.Models;
using System;
using System.Linq;
using System.Data;
using System.Collections.Generic;

namespace RAM.DAL
{
    public class RequestRepository : IRequestRepository<RequestViewModel>
    {

        private RAMcontext context;

        public RequestRepository(RAMcontext context)
        {
            this.context = context;
        }

        public IEnumerable<RequestViewModel> GetRequests()
        {
            var requests = from r in context.RAM_Requests
                    join u in context.Users on r.user_ID equals u.User_ID
                    join res in context.RAM_Resources on r.toResourceID equals res.ID
                    where r.resolved == false
                    select new RequestViewModel()
                    {
                        title = r.title,
                        ID = r.ID,
                        fromResourceID = r.fromResourceID,
                        toResourceID = r.toResourceID,
                        user_ID = r.user_ID,
                        userName = u.First_Name + " " + u.Last_Name,
                        resourceTitle = res.title,
                        requestText = r.requestText,
                        requestDate = r.requestDate
                     };
            /*   }
              catch
              {

               RequestViewModel empty = new RequestViewModel
                  {
                      isEmpty = true
                  };
               return empty;
              }*/
            return requests.ToList().AsEnumerable();
        }

我得到的错误是：

The model item passed into the dictionary is of type 'System.Collections.Generic.List`1[RAM.DAL.Models.RequestViewModel]', but this dictionary requires a model item of type 'RAM.DAL.Models.RequestViewModel'.

Answer 1

根据错误消息，我猜您的操作方法正在向视图发送 RequestViewModel 的集合。但是您的视图被强类型化为 RequestViewModel 的单个实例，而不是集合。这就是您收到此错误的原因。

既然要显示请求的集合，就应该将视图更改为强类型集合。您可以使用 LINQ Any() 方法来确定集合中是否有多个项目传递给视图，并 show/hide 一条消息/ table 来显示数据。

@model IEnumerable<RequestViewModel>
<h1>Dashboard</h1>
@if(!Model.Any())
{
  <p>No records found </p>
}
else
{
  <table>
     <tr>
         <th>Title</th>
         <th>User name </th>
     </tr>
  @foreach(var req in Model)
  {
     <tr>
         <td>@req.title</td>
         <td>@req.userName</td>
     </tr>
  }
  </table>
}

LINQ 存储库和方法 return

LINQ Repository & method return

c#

linq

asp.net-mvc

repository-pattern