AngryHacker AngryHacker - 4 months ago 21
ASP.NET (C#) Question

How does one use Elmah in ASP.NET 5/vNext/Core?

I am a bit confused about how to use Elmah in the ASP.NET 5 / MVC 6 projects. I got the package from nuget and it added

"Elmah.Mvc": "2.1.2"
to dependencies in project.json.

I am not sure where to go from here - back in the day, nuget would add entries to the web.config which is now gone. And I can't seem to find any examples on their github or elsewhere.

Am I missing something simple?

Answer

Instead of using ELMAH, it's not hard to implement error logging manually. This process will catch any exception that occurs in the project and log it to a database table. To do this, add the following to the Configure method in Startup.cs

  if (env.IsDevelopment())
  {
    app.UseDeveloperExceptionPage();
    app.UseBrowserLink();
  }
  else
  {
    app.UseExceptionHandler(builder =>
      {
        builder.Run(async context =>
        {
          context.Response.StatusCode = (int)System.Net.HttpStatusCode.InternalServerError;
          context.Response.ContentType = "text/html";

          var error = context.Features.Get<Microsoft.AspNetCore.Diagnostics.IExceptionHandlerFeature>();
          if (error != null)
          {
            LogException(error.Error, context);
            await context.Response.WriteAsync("<h2>An error has occured in the website.</h2>").ConfigureAwait(false);
          }
        });
      });
  }

Include this in Startup.cs as well:

private void LogException(Exception error, HttpContext context)
{
  try
  {
    var connectionStr = Configuration["ConnectionString"];
    using (var connection = new System.Data.SqlClient.SqlConnection(connectionStr))
    {
      var command = connection.CreateCommand();
      command.CommandText = @"INSERT INTO ErrorLog (Application, Host, Type, Source, Path, Method, Message, StackTrace, [User],  WhenOccured)
    VALUES (@Application, @Host, @Type, @Source, @Path, @Method, @Message, @StackTrace, @User,  @WhenOccured)";
      connection.Open();

      if (error.InnerException != null)
        error = error.InnerException;

      command.Parameters.AddWithValue("@Application", this.GetType().Namespace);
      command.Parameters.AddWithValue("@Host", Environment.MachineName);
      command.Parameters.AddWithValue("@Type", error.GetType().FullName);
      command.Parameters.AddWithValue("@Source", error.Source);
      command.Parameters.AddWithValue("@Path", context.Request.Path.Value);
      command.Parameters.AddWithValue("@Method", context.Request.Method);
      command.Parameters.AddWithValue("@Message", error.Message);
      command.Parameters.AddWithValue("@StackTrace", error.StackTrace);
      var user = context.User.Identity?.Name;
      if (user == null)
        command.Parameters.AddWithValue("@User", DBNull.Value);
      else
        command.Parameters.AddWithValue("@User", user);
      command.Parameters.AddWithValue("@WhenOccured", DateTime.Now);

      command.ExecuteNonQuery();
    }
  }
  catch { }
}

Note that you will have to create a table in your database with the structure used in this function.