(draft) Understanding Yii 3

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Understanding Yii 3

  1. Introduction
  2. Changes overview
  3. Yii 3 composer packages
  4. Running your first Yii 3 powered application


This document is intended for an audience already familiar with Yii2. It's meant to bring together all information related to Yii 3 in one place to make it easier to get on track.

Yii 3 is the second major rewrite of the Yii framework.

Originally started in the 2.1 branch, it was later decided to switch to the 3.X series because of all the backward compatibility breakage. Starting with 3.0, Yii will follow the Sementic Versionning.

This rewrite addresses a lot of issues Yii 2 suffered from, like the framework being too coupled with jQuery, bower, bootstrap. [TODO: add more grieffs about Yii2]

Changes overview

Here are the main changes in Yii 3. You can check the complete CHANGELOG for an exhaustive list.

Source code splitting

The framework source code have been split into several packages, and at its core level, Yii no longer makes assumptions about your development stack, or the features you will be using.

This enable you to cherry pick the packages you need to compose your application.

This re-organisation is also a great news for maintainance, as these packages will be released separately, thus allowing more frequent updates.


The custom PHP class autoloader have been removed in favor of Composer's PSR-4 implementation. This means that in order for Yii to see your classes, you will have to explicitly register your namespace in composer.json. We will see an example later.

PSR compatibility

Yii 3 takes some positive steps following the PHP-FIG recommendations, by implementing the following PSRs:

  • Logging is now compliant with PSR-3
  • Caching is now compliant with PSR-16
  • Dependency Injection is now compliant with PSR-11
Application configuration


Dependencies injection


Yii 3 composer packages

Here are the new packages introduced in Yii 3, which can be found in this official list.

Let's introduce them briefly:

The Framework

This is the new kernel of Yii. It defines the base framework and its core features like behaviors, i18n, mail, validation..

You will rarely want to directly install yiisoft/yii-core. Instead, you will install one or more of the following:

This three packages, considered as Extensions, are responsible for implementing the basic functionnalities of each "channel" they refer to:

  • yii-console implements all that you need to build a console application (the base Controller for commands, the Command helper, ..)
  • yii-web implements all that you need to build a web application (Assets management, Sessions, Request handling ..)
  • yii-rest implements all that you need to build a REST interface (ActiveController, ..)

In Yii 3, libraries do not depend on Yii and are meant to be usable outside the framework. Their package name is yiisoft/something without yii-prefix.

Drivers for yiisoft/db

The various drivers for DB have also been separated into packages:


Extensions depends (at least) on yii-core. Aside from the 3 extensions already encountered above (yii-console, yii-web, yii-api), these packages are available

View rendering engines
Data rendering
JS & CSS Frameworks integration
Yii project template and application bases

This is a very basic Yii project template, that you can use to start your development.

You will probably want to pick one or more of these three starters to install in your project next:

Let's try running the web base template in the next section.

Running your first Yii 3 powered application

Let's try running a web application using Yii 3, and the provided project template.

Installing the project template
composer create-project --prefer-dist --stability=dev yiisoft/yii-project-template myapp
cd myapp

Here's the created structure:

├── README.md
├── composer.json
├── composer.lock
├── config
│   ├── common.php
│   └── params.php
├── docker-compose.yml
├── hidev.yml
├── public
│   ├── assets
│   ├── favicon.ico
│   ├── index.php
│   └── robots.txt
├── runtime
└── vendor

You won't be able to start the web server right away using ./vendor/bin/yii serve, as it will complain about not knowing the "app" class.

In fact, this project template only introduce the bare minimum in your application: Caching, Dependencies injection, and Logging. The template doesn't make an assumption about the kind of application you're building (web, cli, api).

You could start from scratch using this bare template, select the extensions & packages you want to use and start developing, or you can pick one of the three starters provided.

Installing the web starter

Since we're doing a web application, we will need an asset manager. We can pick either one of those:

  • Asset-packagist & composer-merge-plugin (requires only PHP)
  • Foxy (requires npm or yarn)

Let's go with foxy (personal taste since composer is so slow from Tunisia):

composer require "foxy/foxy:^1.0.0"

We can now install the yii-base-web starter and run our application:

composer require yiisoft/yii-base-web
vendor/bin/yii serve

By visiting http://localhost:8080/, you should now see something like this:


Checking back our project structure, nothing really changed, aside from the creation of these three entries:

  • node_modules/
  • package-lock.json
  • package.json

So where do what we see in the browser comes from ?

Exploring yiisoft/yii-base-web structure:

If you explore the folder in vendor/yiisoft/yii-base-web, you will see that the template is in fact a project itself, with this structure:

├── LICENSE.md
├── README.md
├── composer.json
├── config
│   ├── common.php
│   ├── console.php
│   ├── env.php
│   ├── messages.php
│   ├── params.php
│   └── web.php
├── phpunit.xml.dist
├── public
│   └── css
│       └── site.css
├── requirements.php
├── runtime
└── src
    ├── assets
    │   └── AppAsset.php
    ├── commands
    │   └── HelloController.php
    ├── controllers
    │   └── SiteController.php
    ├── forms
    │   ├── ContactForm.php
    │   └── LoginForm.php
    ├── mail
    │   └── layouts
    ├── messages
    │   ├── et
    │   ├── pt-BR
    │   ├── ru
    │   └── uk
    ├── models
    │   └── User.php
    ├── views
    │   ├── layouts
    │   └── site
    └── widgets
        └── Alert.php

The folders and files should make sense to you if you already developed applications using Yii2 and the basic template.

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Written by: Mehdi Achour
Last updated by: samdark
Created on: Dec 16, 2018
Last updated: 4 months ago
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