Asp.net ViewModel 返回 null

Question

我是 Asp.Net Mvc5 和 c# 的新手，我希望能在这里获得一些指导，我一直在努力弄清楚为什么会出现以下错误：

传入字典的模型项的类型为'System.Data.Entity.DbSet1[SoccerTeams.Models.Player]', but this dictionary requires a model item of type 'System.Collections.Generic.IEnumerable1[SoccerTeams.Models.ViewModels.TeamViewModel]'。

但是现在在调试之后我意识到 ViewModel 对象实际上是 returning 所有项目的空值。我创建了一个页面，该页面可以正常工作以添加团队以及该团队的球员。在我的数据库中，球队有一个 table，所有球员都在另一个 table 中，每个球员都有球队名称（球员和球队名称在两个单独的列中），因此它可以与正确的团队。我已经创建了一个 ViewModel，我正在尝试调用该 ViewModel 并能够 return 所有玩家进入视图，以便我可以在列表中显示他们。

我的 "View all players view" 团队控制器如下：

 public ActionResult ViewAllPlayers()
 {
     TeamViewModel teamView = new TeamViewModel();

     return View(teamView);
 }

我的团队模型如下：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace SoccerTeams.Models

{

    // This teams class will be used to represent the teams in the database
    public class Team
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }
        public string TeamName { get; set; }
        public string Coach { get; set; }
        public string Conference { get; set; }
    }
}

我的播放器模型如下：

using System;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace SoccerTeams.Models
{
    public class Player
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }
        public Guid TeamId { get; set; }
        public string Name { get; set; }
    }
}

我的ViewModel如下：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace SoccerTeams.Models.ViewModels
{
    public class TeamViewModel
    {

        public string TeamName { get; set; }
        public string Coach { get; set; }
        public string Conference { get; set; }
        public List<Player> Players { get; set; }
    }
}

我的CreateTeam操作如下：

public async Task<ActionResult> Create(TeamViewModel model, string addfiverows)
        {
            if (ModelState.IsValid)
            {
                if (!string.IsNullOrEmpty(addfiverows)) return View(model);
                var team = new Team { TeamName = model.TeamName, Coach = model.Coach, Conference = model.Conference };

                db.Teams.Add(team);
                var result = await db.SaveChangesAsync();
                if(result > 0)
                {
                    foreach(var player in model.Players)
                    {
                        var p = new Player { Name = player.Name, Id = team.Id };
                        db.Players.Add(p);
                    }
                    result = await db.SaveChangesAsync();
                }
                if(result > 0) return RedirectToAction("Index");
            }
            return View();
        }

我尝试显示的视图如下：

@{
   Layout = "~/Views/Shared/_Layout.cshtml";
}



@model SoccerTeams.Models.ViewModels.TeamViewModel

@{
    ViewBag.Title = "View All Players";
}

<h2>View All Players</h2>


<table class="table">
    <tr>
        <th>
            @Html.DisplayNameFor(model => model.TeamName)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Players)
        </th>
        <th></th>
    </tr>

    @foreach (var item in Model.Players)
    {
        <tr>
            <td>
                @Html.DisplayFor(modelItem => item.TeamName)
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.Players)
            </td>

        </tr>
    }

</table>

通过研究，我认为问题与@model IEnumerable<SoccerTeams.Models.ViewModels.TeamViewModel> 有关。然而，在与@Tony Bao 讨论挑战我的理解之后，我注意到 Viewmodel 实际上是 returning 字段但是具有空值。

我也在寻找任何指南或教程，因为我不仅在寻找解决方案，而且还想更好地理解为什么会发生这种情况以及如何正确使用 ViewModel。

Answer 1

首先将Player集合添加到Team模型：

public class Team
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid Id { get; set; }
    public string TeamName { get; set; }
    public string Coach { get; set; }
    public string Conference { get; set; }
    public virtual ICollection<Player> Players { get; set; }
}

并在 Player 模型中添加 Team:

public class Player
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid Id { get; set; }
    public string Name { get; set; }
    public Guid TeamId { get; set; }
    public virtual Team Team {get; set;}
}

并在 ViewAllPlayers 操作中：

public ActionResult ViewAllPlayers(Guid id)
{
    var team = db.Teams.Include(t => t.Players).Single(t => t.Id == id);
    TeamViewModel teamView = new TeamViewModel
    {
        TeamName = team.TeamName,
        Coach = team.Coach,
        Conference = team.Conference,
        Player = new List<Player>(team.Players)
    };

    return View(teamView);
}

Answer 2

您可以在您的场景中查看 DisplayFor Templates。显示模板（用于显示）和编辑器模板（用于插入和更新）有大量材料。您可以在 google

上搜索

这是我的建议

     public ActionResult ViewAllPlayers()
     {  
        //this should be from your database

        var teamviewer = new TeamViewModel();
        teamviewer.TeamName = "t1";
        teamviewer.Players = new List<Player>() { new Player { PlayerName = "p1" }, new Player { PlayerName = "p2" } };          
        return View();
     }

您的视图模型

   public class TeamViewModel
   {    
        public string TeamName { get; set; }
        public string Coach { get; set; }
        public string Conference { get; set; }
        public List<Player> Players { get; set; }      
   }   

    public class Player
    {    
        public string PlayerName { get; set; }          
    }

在此处创建一个 Displayfor 模板

Views/Shared/DisplayTemplates/Player.cshtml

Player.cshtml

@model SoccerTeams.Models.Player

@Html.DisplayFor(m=>m.PlayerName)

在您的索引页上

@model SoccerTeams.Models.TeamViewModel
<h2>View All Players</h2>


<table class="table">
        <tr>
            <td>
                @Html.DisplayFor(modelItem => modelItem.TeamName)
            </td>
            <td>
                @Html.DisplayFor(modelItem=>modelItem.Players)
            </td>
        </tr>      
</table>

Asp.net ViewModel 返回 null

Asp.net ViewModel returning null

c#

asp.net-mvc

viewmodel

razor