In this article, I will integrate and setup ELMAH to asp.net MVC project. I will finish whole article in 5 different steps. ELMAH stands for Error Logging Modules and Handlers providing application wide error logging facilities. ELMAH is pluggable and easy to implement without changing single line of code. ELMAH work as interceptor of unhandled dotnet exceptions, that display over yellow screen of death. As per Author you can dynamically add ELMAH on running asp.net application without recompile or re-deploy whole application.You can download ELMAH binaries from google code or if you are using nuget then visit ELMAH nuget page.

Install

The best way to install any module to Asp.net MVC project is to use Nuget package Console. You can visit ELMAH nuget page for get latest version command.

Configure

After installing ELMAH , it will automatically update Web.Config file. If it's not so you can add following code to Web.Config file.

<configuration>
<configSections>
    <sectionGroup name="elmah">
      <section name="security" requirePermission="false" type="Elmah.SecuritySectionHandler, Elmah" />
      <section name="errorLog" requirePermission="false" type="Elmah.ErrorLogSectionHandler, Elmah" />
      <section name="errorMail" requirePermission="false" type="Elmah.ErrorMailSectionHandler, Elmah" />
      <section name="errorFilter" requirePermission="false" type="Elmah.ErrorFilterSectionHandler, Elmah" />
    </sectionGroup>
</configSections>

<system.web>   
    <httpModules>
      <add name="ErrorLog" type="Elmah.ErrorLogModule, Elmah" />
      <add name="ErrorMail" type="Elmah.ErrorMailModule, Elmah" />
      <add name="ErrorFilter" type="Elmah.ErrorFilterModule, Elmah" />
    </httpModules>
</system.web>

<system.webServer>
<modules>
      <add name="ErrorLog" type="Elmah.ErrorLogModule, Elmah" preCondition="managedHandler" />
      <add name="ErrorMail" type="Elmah.ErrorMailModule, Elmah" preCondition="managedHandler" />
      <add name="ErrorFilter" type="Elmah.ErrorFilterModule, Elmah" preCondition="managedHandler" />
</modules>
</system.webServer>
<elmah>
    <security allowRemoteAccess="false" />
    <errorLog type="Elmah.SqlErrorLog, Elmah" connectionStringName="YourConnectionStringName" />
</elmah>
    <location path="elmah.axd" inheritInChildApplications="false">
    <system.web>
      <httpHandlers>
        <add verb="POST,GET,HEAD" path="elmah.axd" type="Elmah.ErrorLogPageFactory, Elmah" />
      </httpHandlers>
      <!--
      <authorization>
        <allow roles="admin" />
        <deny users="*" /> 
      </authorization>
      --> 
    </system.web>
    <system.webServer>
      <handlers>
        <add name="ELMAH" verb="POST,GET,HEAD" path="elmah.axd" type="Elmah.ErrorLogPageFactory, Elmah" preCondition="integratedMode" />
      </handlers>
    </system.webServer>
  </location>
</configuration>
Usage Now, It's time to use and test elmah for application. Generate exception in Home Controller
public ActionResult Index()
{
   throw new Exception("This is test Exception");
          
   return View();
}

after generating exception check your elmah like http://www.example.com/elmah.axd
Here is our output

Security

In addition ELMAH provides seamless security feature to prevent unauthorized access. Please read our next article to make your elmah secure.

Filtering

ELMAH identify and store exceptions in different category, you can make or edit ELMAH error screen with different filters which we will discuss in our next ELMAH series.

Notification

You can setup ELMAH email notification when any exception occurs. To unable notification option you must include below code

Add ErrorMail module
<httpModules>
    <add name="ErrorMail" type="Elmah.ErrorMailModule, Elmah"/>
</httpModules>

Add SMTP Setting
<system.net>
    <mailSettings>
        <smtp deliveryMethod="network">
            <network host="..." port="25" userName="..." password="..." />
        </smtp>
    </mailSettings>
</system.net>
 
or
<elmah>
<errorMail from="..." to="..."  async="true" smtpServer="..." smtpPort="25" userName="..." password="..." />
</elmah>

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In this tutorial, I will show you how to make simple application in ASP.NET MVC using Select2. The infinite scrolling feature has also been implemented with server side options population. Select2 is very useful for dropdown lists with large datasets.

Why Select2 :

• Using this jQuery plugin for dropdown lists, you can implement features such as option grouping, searching, infinite scrolling, tagging, remote data sets and other highly used features.
• To use select2 in web projects, you just have to include JavaScript and CSS files of Select2 in your website.
• Current version of select2 is 4.0.0. You can easily include these files by installation of NuGet package ‘Select2.js’ from NuGet package manager.

Steps of Implementation:
1. Create a blank ASP.NET MVC project, and install NuGet packages Select2.js, jQuery and jQuery Unobtrusive.
2. Add one controller with the name ‘HomeController’ and add view for default method ‘Index’.
3. Create new class in Models folder ‘IndexViewModel.cs as shown below:

public class IndexViewModel
{
   [Required(ErrorMessage="Please select any option")]
   public string OptionId { get; set; }
}

4. Bind ‘Index.cshtml’ view with IndexViewModelClass as model, by adding the following line in Index view:

@model Select2InMvcProject.Models.IndexViewModel

5. In ‘Index.cshtml’, include the css and js files below:

<link href="~/Content/css/select2.css" rel="stylesheet" />
<script src="~/Scripts/jquery-2.1.4.js"></script>
<script src="~/Scripts/select2.js"></script>
<script src="~/Scripts/jquery.validate.js"></script>
<script src="~/Scripts/jquery.validate.unobtrusive.js"></script>

6. Write the following code in the Index view for creation of select list:

@using (Html.BeginForm())
{
   <br /><br />
   @Html.DropDownListFor(n => n.OptionId, Enumerable.Empty<SelectListItem>(), new { @id = "txtOptionId", @style = "width:300px;" })
//Created selectlist with empty enumerable of SelectListItem and given //id as “txtOptionId”
   @Html.ValidationMessageFor(n => n.OptionId)
//Adds span of validation error message
   <br /><br />
<button type="submit">Submit</button>
   <br /><br />
}

7. For applying Select2 to the dropdown list created above, fetching data from server side and for infinite scroll, use the jQuery code below in Index view:

<script type="text/javascript">
   $(document).ready(function () {
       var pageSize = 20;
       var optionListUrl = '@Url.Action("GetOptionList", "Home")';
//Method which is to be called for populating options in dropdown //dynamically
       $('#txtOptionId').select2(
       {
           ajax: {
               delay: 150,
               url: optionListUrl,
               dataType: 'json',
               data: function (params) {
                   params.page = params.page || 1;
                   return {
                       searchTerm: params.term,
                       pageSize: pageSize,
                       pageNumber: params.page
                   };
               },
               processResults: function (data, params) {
                   params.page = params.page || 1;
                  return {
                       results: data.Results,
                       pagination: {
                           more: (params.page * pageSize) < data.Total
                       }
                   };
               }
           },
           placeholder: "-- Select --",
           minimumInputLength: 0,
           allowClear: true,
   });
});
</script>

8. Create new class in Models folder with name ‘Select2OptionModel’ and add the two classes below:

public class Select2OptionModel
{
       public string id { get; set; }
       public string text { get; set; }
}
public class Select2PagedResult
{
       public int Total { get; set; }
       public List<Select2OptionModel> Results { get; set; }
}

9. Create one new folder with name ‘Repository’ in the solution, and add new class in that folder with name ‘Select2Repository. The functions in this class are mentioned below:

public class Select2Repository
   {
       IQueryable<Select2OptionModel> AllOptionsList;
public Select2Repository()
{
           AllOptionsList = GetSelect2Options();
}
IQueryable<Select2OptionModel> GetSelect2Options()
                  {
                                     string cacheKey = "Select2Options";
                                     //check cache
                                     if (HttpContext.Current.Cache[cacheKey] != null)
                                     {
return (IQueryable<Select2OptionModel>)HttpContext.Current.Cache[cacheKey];
                                     }
                                     var optionList = new List<Select2OptionModel>();
                                     var optionText = "Option Number ";
                                     for (int i = 1; i < 1000; i++)
                                     {
                                     optionList.Add(new Select2OptionModel
                                     {
                                               id = i.ToString(),
                                               text = optionText + i
                                     });
                                   }
                                   var result = optionList.AsQueryable();
                                     //cache results
                                     HttpContext.Current.Cache[cacheKey] = result;
                                     return result;}
 
List<Select2OptionModel> GetPagedListOptions(string searchTerm, int pageSize, int pageNumber, out int totalSearchRecords)
                  {
                                     var allSearchedResults = GetAllSearchResults(searchTerm);
                                     totalSearchRecords = allSearchedResults.Count;
return allSearchedResults.Skip((pageNumber - 1) * pageSize).Take(pageSize).ToList();
                  }
                  List<Select2OptionModel> GetAllSearchResults(string searchTerm)
                  {

                                     var resultList = new List<Select2OptionModel>();
                                      if (!string.IsNullOrEmpty(searchTerm))
resultList = AllOptionsList.Where(n => n.text.ToLower().Contains(searchTerm.ToLower())).ToList();
                                     else
                                     resultList = AllOptionsList.ToList();
                                     return resultList;
                  }
                  public Select2PagedResult GetSelect2PagedResult(string searchTerm, int pageSize, int pageNumber)
                  {
                                     var select2pagedResult = new Select2PagedResult();
                                     var totalResults = 0;
                                     select2pagedResult.Results = GetPagedListOptions(searchTerm,
pageSize, pageNumber, out totalResults);
                                     select2pagedResult.Total = totalResults;
                                     return select2pagedResult;
}
}

10.  In HomeController class, create new method as shown below:

public JsonResult GetOptionList(string searchTerm, int pageSize, int pageNumber)
{
     var select2Repository = new Select2Repository();
     var result = select2Repository.GetSelect2PagedResult(searchTerm, pageSize, pageNumber);
     return Json(result, JsonRequestBehavior.AllowGet);
}

11. Once you are done with coding, you can build and run the project. The output will be shown as below:

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