Group By Linq ASP.NET

Question

我目前显示数据库中的错误列表。从下图中可以看出，有许多错误共享相同的应用程序名称。

我想将所有同名的错误组合在一起，只显示该应用程序名称的一个错误，而不是全部错误。

我在这里看到了与我正在做的事情有关的其他问题，但没有人给我答案。

这是我目前的代码。

控制器

public ActionResult Index(string sortOrder, string searchString, string currentFilter, int? page)
    {
        ViewBag.CurrentSort = sortOrder;
        ViewBag.DateSortParm = sortOrder == "Date" ? "date_desc" : "Date";

        if (searchString != null)
        {
            page = 1;
        }
        else
        {
            searchString = currentFilter;
        }

        ViewBag.CurrentFilter = searchString;

        var applications = from s in db.ElmahErrors
                     select s;


        if (!String.IsNullOrEmpty(searchString))
        {
            applications = applications.Where(s => s.Application.Contains(searchString));
        }

        switch (sortOrder)
        {
            default:
                applications = applications.OrderBy(x => x.Application).ThenByDescending(s => s.TimeUtc);
                break;
        }


        int pageSize = Int32.Parse(System.Configuration.ConfigurationManager.AppSettings["DefaultPageSize"]);
        int pageNumber = (page ?? 1);
        return View(applications.ToPagedList(pageNumber, pageSize));
    }  

视图

@model PagedList.IPagedList<DataIntelligence.Models.ElmahError>
@using PagedList.Mvc;
<link href="Content/PagedList.css" rel="stylesheet" type="text/css" />

@{
    ViewBag.Title = "Application Error Dashboard";
}

<div class="jumbotron">
    <h2>Application Error Dashboard</h2>
</div> 
@using (Html.BeginForm("Index", "Application", FormMethod.Get))
{
    <p>
        Find by Application: @Html.TextBox("SearchString", ViewBag.CurrentFilter as string)
        <input type="submit" value="Search" />
    </p>
}
<table>
    <tr>
        <th>
            Application
        </th>
        <th>
            Host
        </th>
        <th>
            Type
        </th>
        <th>
           Date
        </th>
        <th>
            Message
        </th>

    </tr>

@foreach (var item in Model) {
    <tr>
        <td>
            <a href="@Url.Action("Details", new { id=item.ErrorId})"> @Html.DisplayFor(modelItem => item.Application) </a>      
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Host)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Type)

        </td>
        <td >
            @Html.DisplayFor(modelItem => item.TimeUtc)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Message)
        </td>


    </tr>
}

</table>
<br />
Page @(Model.PageCount < Model.PageNumber ? 0 : Model.PageNumber) of     @Model.PageCount

@Html.PagedListPager(Model, page => Url.Action("Index", new { page, sortOrder = ViewBag.CurrentSort, currentFilter = ViewBag.CurrentFilter }))  

如何更改此代码以实现我想要的目标？

提前致谢。

Answer 1

如果替换：

var applications = from s in db.ElmahErrors
                 select s;

使用：

var applications = db.ElmahErrors
  .GroupBy(s => s.Application)
  .Select(grp => grp.FirstOrDefault());

然后查询将只处理每个应用程序的一个元素。

您可能还希望在以后的状态下执行此分组，如果ElmahErrors中有某些元素要根据其他条件过滤掉，以确保您没有碰巧过滤掉不同的当另一个具有相同Application的项目未被过滤时选择的项目。

Answer 2

您应该查看“MoreLinq＆＃39;”，也许他们的DistinctBy会提供您需要的答案。它在NuGet中可用。 MoreLINQ's DistinctBy for C#

应该是这样的：

List<ElmahErrors> distinctByError = db.ElmahErrors.DistinctBy(x => x.Message).ToList();

Answer 3

尝试此查询

var applications = from s in db.ElmahErrors
 group c by new
    {
        s.Application,
        s.Host,
        s.Type, 
        s.Date,
        s.Message
    } into gcs
    select new ElmahErrors()
    {
        gcs.key.Application,
        gcs.key.Host,
        gcs.key.Type, 
        gcs.key.Date,
        gcs.key.Message
    };

Answer 4

var results = from a in applications
              group a by a.Application into g
              select new { Application = g.Key, Count = g.Count(), LastDate = g.Max(d=>d.Date) };

或者，如果你想通过更多的电影分组：

 var results = from a in applications
                  group a by new {a.Application, a.Message} into g
                  select new { Application = g.Key.Application, Message = g.Key.Message, Count = g.Count(), LastDate = g.Max(d=>d.Date) };