Category: ASP.NET Core

Fat Controller CQRS Diet: Vertical Slices

Derek Comartin 6 Comments

This post is in my Fat Controller CQRS Diet series. It demonstrates how to thin your controllers by implementing commands and queries using the MediatR library.  Specifically in this post, I’ll look at organizing your code by vertical slices.

I’m converting the MusicStore application that’s using ASP.NET Core MVC.   All the source code is available on GitHub.

If you’re new to this series, here are earlier posts to get up to speed:

  1. Overview of Series
  2. Simple Query
  3. Simple Command
  4. Command Pipeline
  5. Notifications

Organize by Feature

Feature Slices or Vertical Slices are the terms I’ve heard the most for what I call Organize by Feature.

I’ve just always characterized as organizing all relevant code and files from a command or query into a specific folder or hopefully single file.

I generally stay away from creating layers so the term Vertical Slices does make a lot of sense.

Whatever our feature slice is, it surely makes sense to keep all that code together.

Single File

If you’ve seen the code related to my Command Pipeline or Notifications posts, then you should already be able to tell where I’m heading in terms of organization.

I generally like to keep the command/query and it’s associated handler all within the same file.  In the case of our logging handler, I was also keeping it in this file.

Pretty simple.  One file for everything related to a command or query.

Controllers & Views

Well almost.  What I hadn’t really moved were the controllers or views.  So let’s do that now.

Controllers are pretty easy since by default they can live anywhere within your project. ASP.NET MVC Core will just pick them up.

Let’s work on our Home Query.  We will simply create a HomeController within our Home.cs file that currently contains our query and our handler.

Because we are no longer using the default routing, I’ve added the HttpGet attribute to the method to keep the route intact to what it was prior.

View Locator

By default, ASP.NET Core MVC will look in the ~/Views/ folder with default conventions.  But we want to put our view right along side our Home.cs file in our Features folder.

So I’ve moved all of the view files into our Features folder.  Our solution now looks like this:

 

In order to tell ASP.NET where our views are now at, we can implement the IViewLocationExpander

Now in the  IServiceProvider ConfigureServices(IServiceCollection services) method from our Startup.cs, we can can configure to use our new locator.

That’s it!

We now have one file that contains our controller, query and handler.  And right along side it we have our associated view.

Comments

All the source code for this series is available on GitHub.GitHub

I love hearing your comments, questions and recommendations as it usually leads me down to other blog posts.  Please post a comments or on Twitter.


Fat Controller CQRS Diet: Notifications

Derek Comartin 12 Comments

CQRS NotificationsThis post is in my Fat Controller CQRS Diet series. It demonstrates how to thin your controllers by implementing commands and queries using the MediatR library.

I’m converting the MusicStore application that’s using ASP.NET Core MVC.   All the source code is available on GitHub.

If you’re new to this series, here are earlier posts to get up to speed:

  1. Overview of Series
  2. Simple Query
  3. Simple Command
  4. Command Pipeline

Logging

In the my previous Command Pipeline example, I leveraged StructureMap and the decorator pattern to setup a pipeline.

My pipeline would invoke the actual command handler as well as any classes that implemented the correct IPostRequestHandler<TRequest, TResponse>.

This enabled us to create a AddToCartLogHandler which did our logging that was originally in the ShoppingCartController.AddToCart action method.

Notifications

Another way to implement this is with a Notification (event).

MediatR has this concept built in with a couple interfaces INotification, IAsyncNotification

The concept and how it works with MediatR very similar as a request (Command or Query) and it’s appropriate handler.  The difference with a Notification is it can have many handlers.

  • Request: only one handler
  • Notification: zero to many handlers

Implementation

I’m going to jump back to our AddToCart command.  Instead of it using an IPostRequestHandler<AddToCart, Unit> that I created for our pipeline, I’m going to instead create a notification and publish that notification from MediatR.

First, we need to create a class to represent our notification.  All the class will contain is a property to specify the AlbumId that was added to the shopping cart.

Now we will create a Notification Handler that will accept this new notification object and do the logging.

Finally, our last piece is to Publish a new AlbumAddedToCart notification to MediatR.  We can do so in our AddToCartHandler .

Comments

All the source code for this series is available on GitHub.GitHub

Which do you prefer, Pipeline or notifications? Let me know in the comments or on Twitter.


Fat Controller CQRS Diet: Command Pipeline

Derek Comartin 4 Comments

Command PipelineThis post is in my Fat Controller CQRS Diet series demonstrating how to thin your controllers by implementing commands and queries using the MediatR library.

For demonstration, I’m converting the MusicStore application that’s using ASP.NET Core MVC.   All the source code is available on GitHub.

If you’re new to this series, here are earlier posts in this series:

  1. Overview of Series
  2. Simple Query
  3. Simple Command

Pipelines

In both the new  Query and Commands handlers wrote in prior posts, there was one thing standing out that really didn’t belong.

Logging

For reference, here was our AddToCartHandler that did some logging at the end of the method.

This really isn’t a concern of our AddToCartHandler.  One way we can separate logging out is by having our Command go through another handler after it’s been executed.  If we think about this a bit more broad, we can take it a step further and create a pipeline for our Command that can go through various handlers prior and after the main AddToCartHandler.

Video

If you prefer, I have a video tutorial that follows this blog post.

Decorators

One way to accomplish this is to use Decorators.  A decorator is nothing more than wrapper around our main handler.

In our example, we are going to use StructureMap.  In your project.json, add the following dependencies.

Next in our Startup.cs we are going to configure StructureMap in the IServiceProvider ConfigureServices(IServiceCollection) method.

The gist is we are going to Decorate/Wrap any ICancellableAsyncRequestHandler<TRequest,TResponse> in a Pipeline<TRequest,TResponse> (which we will create next).

Here is our implementation of the Pipeline<TRequest,TResponse>

It will take the primary request as the first argument in the ctor, and then a array of IPostRequestHandler<TRequest,TResponse>, which we will create next to define our logging handlers.

Log Handler

We now have everything in place to separate the logging from our AddToCartHandler.

All we need to know is create a class that will implement IPostRequestHandler<AddToCart,Unit> and it will be invoked after the AddToCartHandler.

Now we can jump back over to our AddToCartHandler and remove the ILogger and the logging code.

Validation, Authorization, Whatever

Hopefully now you can see that we could extend this to have pre-handlers that may do data validation, authorization or whatever other responsibilities that probably shouldn’t be in your main handler.

Comments

All the source code for this series is available on Github.GitHub

If have another way of creating a pipeline or separating concerns from your handlers, please leave comment or let me know on twitter.