Why changes in Phoenix 1.3 are so important?

Phoenix Framework always has been awesome. But it was never as awesome as the new 1.3 release (which is rc1 right now actually).

There are a lot of significant changes. Chris McCord made a great job writing a complete migrating guide. Inspired by it and by the talk Chris gave at the LonestarElixir this article will try to guide through the most important changes in the phoenix project.

Let’s get started!

Problems to solve

phoenix is new. And naturally it has some issues. The core team has worked really hard to solve some of the most curial ones in the newest release. So what are these issues?

Web folder is pure magic

When working on a project using phoenix, you have two places for the source code: lib/ and web/. The concept is:

1. Put all your business logic and utilities inside lib/
2. Put everything that relates with your web-interface (controllers, views, templates) inside the web/ folder

But is that message clear enough for the developers? I don’t think so.

Where did this web/ folder come from? Is it a phoenix special? Or other frameworks use it too? Should I even use lib/ with phoenix projects or is it reserved for some deep magic? All these questions ran through my head after my first encounter with phoenix.

Before version 1.2 web/ was the only one to auto-reload. So, why should I create any files inside lib/ and restart a server when I can put it somewhere inside web/ to reload quickly?

Which brings us to even more important questions: do my model files (let’s call them models in this particular context) belong to the web part of my application or to my core logic? Is it possible to separate my logic into different domains or apps (like in django)?

These questions are left unanswered.

Business logic in controllers

Moreover, the boilerplate code, which comes with the phoenix itself, was promoting the other way of doing things. One would get these lines of code with the newly generated project:

Old boilerplate code

What should a developer do when an email should be sent to a user after a successful update? The controller itself asks to be extended. Just put a new line of code before render/4. But that’s a wrong way of doing things. And it was kind of promoted by the phoenix itself.

One extra line in the controller is fine, that’s not a big deal. All the problems come when the application grows. It becomes untestable, unmaintainable, and self-repeating.

Schemas are not models

At some point for no particular reason ecto ‘s schemas started to be called “models”. What is the difference between a “model” and a “schema”? Schema is just a way to define a structure - a database structure at this particular case. Models as a concept are much more complex than schemas. Models should provide a way to manipulate data and perform different actions, like models in django. elixir as a functional language is not suited for the “model” concept, so it was deprecated a long time ago in the ecto project.

Files inside models/ were not organized. When your application grew, it became a complete mess. How these files are bounded? What is the context we use them in? It was hard to figure that out.

Furthermore, models/ folder was considered as a place to put your business logic, which is a normal thing to do in other languages and frameworks. We have a concept of “fat models”, with which we are already familiar. But in phoenix it is just one more wrong way of doing it.

Solutions

A lot has changed since the last major release. The easiest way to show all the changes is by example.

Requirements

This tutorial assumes that you have elixir-1.4 up and running. No? Then install it!

Installation

Firstly, you would need to install new phoenix release:

» mix archive.install https://github.com/phoenixframework/archives/raw/master/phx_new.ez

Creating new project

When installation is completed, it is time to check that everything is in place. mix help will return you something like this:

mix phoenix.new       # Creates a new Phoenix v1.1.4 application
mix phx.new           # Creates a new Phoenix v1.3.0-rc.1 application using the experimental generators

That’s where the first change comes in: new generators. Old generators were named phoenix while the new ones are named simply phx. Less typing. And a new message to the developers: these generators are new, they will do new things to your codebase.

Then, it is time to create new project’s structure by running:

mix phx.new medium_phx_example --no-html --no-brunch

Before we see any results of this command, let’s discuss the options. --no-html removes some specific components so phx.gen.html will no longer work. But we are building json API and we won’t need any html. Similarly --no-brunch means: do not generate brunch files for static asset building. When choosing this option, you will need to manually handle JavaScript dependencies if building html apps.

Changes

Web folder

Looking at your newly generated files you may be wondering: where is the web/ folder? Well, here is the second change. And it’s big. Now your web/ folder lives inside lib/. This web/ folder was special; a lot of people misunderstood its main purpose, which was containing web interface for your application. It’s not a place for your business logic. Now things are clear. Put everything inside lib/. And put only your controllers, templates and views inside the new web/.

That’s how it looks:

lib
└── medium_phx_example
    ├── application.ex
    ├── repo.ex
    └── web
        ├── channels
        │   └── user_socket.ex
        ├── controllers
        ├── endpoint.ex
        ├── gettext.ex
        ├── router.ex
        ├── views
        │   ├── error_helpers.ex
        │   └── error_view.ex
        └── web.ex

Where medium_phx_example is the name of the current app. There can be many apps. So now all the code lives inside the same folder.

The third change will reveal itself shortly after looking at the web.ex file:

Example of web.ex

phoenix now creates .Web namespace for us, which pairs really well with the new folder structure.

Creating schema

That’s the forth change and my favorite one so far. Previously we had a web/models/ folder, which was used to store schemas. Now “model” concept is completely dead. A new philosophy of doing things is introduced:

1. Context is used to store multiple schemas
2. Context is used to provide a public external API. In other words, it defines what can be done to your data
3. Schema is just a description of your data

Our application would contain just one context: audios. Let’s start by creating Audio context with Album and Song schemas:

» mix phx.gen.json Audio Album albums name:string release:utc_datetime
» mix phx.gen.json Audio Song songs album_id:references:audio_albums name:string duration:integer

The syntax of this generator has also changed. Now it requires the context name to be the first argument. Also take note of the audio_albums notation, albums schema is prefixed with the context name. And here’s what happens to the project structure after we run two generators:

lib
└── medium_phx_example
    ├── application.ex
    ├── audio
    │   ├── album.ex
    │   ├── audio.ex
    │   └── song.ex
    ├── repo.ex
    └── web
        ├── channels
        │   └── user_socket.ex
        ├── controllers
        │   ├── album_controller.ex
        │   ├── fallback_controller.ex
        │   └── song_controller.ex
        ├── endpoint.ex
        ├── gettext.ex
        ├── router.ex
        ├── views
        │   ├── album_view.ex
        │   ├── changeset_view.ex
        │   ├── error_helpers.ex
        │   ├── error_view.ex
        │   └── song_view.ex
        └── web.ex

What are the main changes in the structures compared to the previous version?

1. Now schemas do not belong to web/ at all
2. models/ folder is gone
3. Schemas are now separated by context, which defines how they are bounded together

And schemas right now are nothing more than a table description. That’s what a schema is in the first place. Here’s what our schemas look like:

album.ex

song.ex

Everything except schema declaration is gone. No required_fields , no changeset/2 function or any other functions and logics. It does not even generate belongs_to for you.

So, it is pretty clear now: this is not a place for your business logic. It is all handled by the context, which looks the following way:

audio.ex

It also sends a clear message: this is the place where one should put their code! But be careful, context files can grow long. Split them in several modules in that case.

Using controller

Previously we had a lot of code in the controller by default. It was easy for a developer to extend the boilerplate code. Here comes the fifth change. Since the new release the boilerplate code in the controller has been reduced and refactored:

New boilerplate code

There are only three meaning lines of code in the update/2 action right now. Controllers currently use contexts directly, which makes them a very thin layer in the application. It is hard to find a place for some extra logic in the controller. Controllers do not even handle errors.

Errors are designed to be handled by a special fallback_controller. This new concept is the sixth change. It allows to have all error handlers and error codes in the one place:

fallback_controller.ex

What happens when the result from Audio.update_album(album, album_params) does not match with {:ok, %Album{} = album}? In this situation a controller defined in action_fallback is called. And a proper call/2 is pattern matched, which returns a valid response. Nice and easy. No more exception handling in the controller.

Conclusion

All things said the changes introduced are quite exciting. Hope this article was helpful and encouraged you to get out there and use Phoenix Framework to its maximum.

Keep in touch with me on GitHub:

sobolevn (Sobolev Nikita)