In order to install the Nancy async beta with NuGet, we need to add the feed from https://www.myget.org/F/nancyasync/ as a source in the package manager in Visual Studio.

Next, update the Nancy NuGet package to the newest beta version. This will add async support to Nancy. In order to update to a beta version, include the IncludePrerelease option in the NuGet command:

PM> Update Nancy –IncludePrerelease

Run all tests to see if updating the Nancy package had any negative effects. The RequestLoggingTests.Should_log_error_on_failing_request test will fail because the error pipeline is now async. Due to the way in which .NET handles propagating exceptions in async code, FormatException we are expecting to log is wrapped inside AggregateExcption. We can get the error logging we want by changing just one line in the bootstrapper as follows:

    private void LogUnhandledExceptions(IPipelines pipelines)
    {
      pipelines.OnError.AddItemToStartOfPipeline((ctx, err) =>
      {
        log.ErrorException(string.Format("Request {0} \"{1}\" failed. Exception: {2}", ctx.Request.Method, ctx.Request.Path, err.ToString()), err);
        return null;
      });
    }

We are now ready to take advantage of async in our route handlers, so we go into the TodosModule project and change the handler for "/" to the following:

      Get["/", true] = async (_, __) =>
      {
        var allTodos = await todoStore.GetAll();
        return Negotiate
          .WithModel(allTodos.Where(todo => todo.userName == Context.CurrentUser.UserName).ToArray())
          .WithView("Todos");
      };

We changed the signature of the delegate handling the route and also added an extra parameter to the route. We will get back to these changes in the following How it works… section. For now, we need to compile the code again. That is, we need to make the todosStore.GetAll()call return a Task. The IDataStore interface becomes as follows:

  public interface IDataStore
  {
    Task<IEnumerable<Todo>> GetAll();
    long Count { get; }
    bool TryAdd(Todo todo);
    bool TryRmove(int id, string userName);
    bool TryUpdate(Todo todo, string userName);
  }

As an exercise, you now have to update your implementation of IDataStore accordingly. The updated version of the MongoDataStore class is in the code download for this recipe. Furthermore, you will need to update a few tests that fake out the call as we just made async. In each of these tests, the fake return values have to be wrapped in the Task objects and these tasks need to be started. As an example, look at the following test from DataStoreTests:

    [Fact]
    public void Should_remove_deleted_todo_from_datastore()
    {
      var returnValue = new Task<IEnumerable<Todo>>(() => new [] { new Todo { id = 1 }, new Todo { id = 2 } });
      returnValue.Start();
      A.CallTo(() => fakeDataStore.GetAll())
       .Returns(returnValue);

      sut.Delete("/todos/1");

      A.CallTo(() => fakeDataStore.TryRmove(1, A<string>._)).MustHaveHappened();
    }

When you have made similar changes to all tests, they should all pass again, and the application should work just like it used to except now one of our handlers is asynchronous.