Question

使用ASP.NET MVC，.NET Framework 4.5.2，SQL DB的实体数据模型，Visual Studio 2017。

我有一个从ADO.NET生成的类（来自数据库的EF Designer）：

BookInfo.cs

 namespace LibraryMS
{
 using System;
 using System.Collections.Generic;

public partial class BookInfo
{
    public string BookID { get; set; }
    public string Title { get; set; }
    public string Author { get; set; }
    public string Publisher { get; set; }
    public string PublishDate { get; set; }
    public string Edition { get; set; }

    public virtual Inventory Inventory { get; set; }
}
}

数据库设计在＆＃34; BookID＆＃34;在BookInfo表中有一个外键＆＃34; BookID＆＃34;在库存表中。为了更新＆＃34; BookID＆＃34;引用的广告资源属性，我继续查询列表并更新正确的实例。

更新广告资源页面的屏幕截图：

当登陆页面输入信息时，点击＆＃34;创建＆＃34;时会调用[HttpGet] UpdateInventory（）。按钮如上图所示，调用[HttpPost] UpdateInventory（...）。

控制器中的逻辑/代码：

    [HttpGet]
    public  ActionResult UpdateInventory()
    {
        return View();
    }


    [HttpPost]
    public async Task<ActionResult> UpdateInventory(string bookID, string ttlIn, string lowin, string outnow)
    {
        var bf = await SqlRestApiHelper.searchFromBooks(bookID);

        bf.Inventory.TotalIn = Convert.ToInt16(ttlIn);
        bf.Inventory.LowIn = Convert.ToInt16(lowin);
        bf.Inventory.Out = Convert.ToInt16(outnow);
        await SqlRestApiHelper.UpdateBookInfoInventory(bf.Inventory);

        await SqlRestApiHelper.SaveChanges();
        return View("All");            
    }

 [HttpGet]
    public async Task<ActionResult> All()
    {
        return View(await SqlRestApiHelper.getAllBooksInfo(0, 10));
    }

SqlRestApiHelper.cs

namespace LibraryMS
{
public static class SqlRestApiHelper
{
   private static libraryDBEntities entities = new libraryDBEntities();


    public static async Task<LibraryMS.BookInfo> searchFromBooks(string id)
    {
       return entities.BookInfoes.ToList().Find(book => book.BookID == id);
    }

    public static async Task UpdateBookInfoInventory(LibraryMS.Inventory inv)
    {
        var newInv = inv;

        var el = entities.BookInfoes.ToList().Find(x => x.Inventory.BookID == newInv.BookID);
        if (el != null) 
        {
            el.Inventory.TotalIn = newInv.TotalIn;
            el.Inventory.LowIn = newInv.LowIn;
            el.Inventory.Out = newInv.Out;
            // the above updates the list item referenced
        }

    }

    public static async Task SaveChanges()
    {
       await entities.SaveChangesAsync();
    }

 public static async Task<IPagedList<BookInfo>> getAllBooksInfo(int page, int itemsPerPage)
    {
        List<BookInfo> bookinfo = new List<BookInfo>();

            bookinfo = (from o in entities.BookInfoes
                      orderby o.Title descending //use orderby, otherwise Skip will throw an error
                      select o)
                      .Skip(itemsPerPage * page).Take(itemsPerPage)
                      .ToList();
        int totalCount = bookinfo.Count();//return the number of pages
        IPagedList<BookInfo> pagebooks = new StaticPagedList<BookInfo>(bookinfo, page + 1,10,totalCount);
        return pagebooks;//the query is now already executed, it is a subset of all the orders.
    }

抛出空的异常：

all.cshtml视图页面的代码：

 @model PagedList.IPagedList<LibraryMS.BookInfo>
 @using PagedList.Mvc;
 @{
ViewBag.Title = "All";
 }

 <h2>all</h2>

 <table class="table">

 @foreach (var item in Model) {
 <tr>
    <td>
        @Html.DisplayFor(modelItem => item.Title)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.Author)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.Publisher)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.PublishDate)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.Edition)
    </td>

    <td>
        @Html.ActionLink("Details","Details",new { item.BookID})
    </td>
</tr>
 }

 </table>

 @Html.PagedListPager(Model, page => Url.Action("All","BookInfoController", new { page }))

Answer 1

您的视图引发错误，因为您在不传递模型的情况下返回视图，而是在不传递模型的情况下使用return View("All") 正确的方法是通过视图传递模型，你可以这样做 View("ViewName", ModelData);

在你的情况下

return View("All", await SqlRestApiHelper.getAllBooksInfo(0, 10));

对于保存部分我不知道为什么，但我可以看到很少的错误，首先，如果书没有库存信息怎么办？它将抛出null错误，因此首先检查是否为null，创建新库存，如果不相应更新这是我将如何做到这一点

 public static async Task UpdateBookInfoInventory(Inventory inv)
 {
    var newInv = inv;
     // get book info
    var el = entities.BookInfoes.FirstOrDefault(x => x.BookID == inv.BookID);
    if (el != null) 
    {
         if(el.Inventory != null)
       {
           // update accordingly
        el.Inventory.TotalIn = newInv.TotalIn;
        el.Inventory.LowIn = newInv.LowIn;
        el.Inventory.Out = newInv.Out;
        // the above updates the list item referenced
    }
    else
      { 
        /// add new if null 
         el.inventory = newInv;  
     }
   await SqlRestApiHelper.SaveChanges();

}

Answer 2

作为第一步，将断点放在getAllBooksInfo方法中，查看Visual Studio中是否有列表计数。这对你有很大帮助。

作为替代步骤，您还可以使用ToPagedList（pageIndex，pageSize）来解决此错误;方法，我个人使用它，它运作良好

根据您的代码

ToPagedList示例：

     **public static async Task<IPagedList<BookInfo>> getAllBooksInfo(int page, int itemsPerPage)
        {
            List<BookInfo> bookinfo = new List<BookInfo>();

                bookinfo = (from o in entities.BookInfoes
                          orderby o.Title descending //use orderby, otherwise Skip will throw an error
                          select o)
                          .Skip(itemsPerPage * page).Take(itemsPerPage)
                          .ToList();
            int totalCount = bookinfo.Count();//return the number of pages

//changes made to the below line

            IPagedList<BookInfo> pagebooks = bookinfo.ToPagedList(1, 10);


            return pagebooks;//the query is now already executed, it is a subset of all the orders.
        }**

官方来源： https://github.com/troygoode/PagedList

注意：即使使用此方法，也请使用更改行中的断点检查是否从数据库获取数据。

希望这肯定会解决您的问题，请让我知道想法或反馈

由于

KARTHIK

在视图中抛出空例外

2 个答案: