Running applications

After installing Yii, you have a working Yii application that can be launched via ./yii serve and then accessed via the URL http://localhost:8080/. This section will introduce the application’s built-in functionality, how the code is organized, and how the application handles requests in general.

Info: For simplicity, throughout this “Getting Started” tutorial use “serve” command. It shouldn’t be used to serve the project in production. When setting up a real server, use app/public as the document root.

Note that unlike the framework itself, after you install a project template, it’s all yours. You’re free to add or delete code and overall change it as you need.

Functionality

The application installed has only the homepage, displayed when you access the URL http://localhost:8080/. It shares a common layout that could be reused on further pages.

Additionally, to the web application, there is a console script accessible via ./yii. This script can be used to run background and maintenance tasks for the application, which are described in the Console Application Section.

Application Structure

The most important directories and files in your application are (assuming the application’s root directory is app):

config/                   Configuration files.
    common/               Configs applied to both console and web.
        di/               DI container configuration.
        aliasess.php      Aliases.
        params.php        Various parameters used in DI configs.
        routes.php        Application routes.
    console/              Configs applied to console.
        commands.php      Registered console commands.
        params.php        Various parameters used in DI configs.
    web/                  Configs applied to web.
       di/                DI container configuration.
       params.php         Various parameters used in DI configs.
    environments/         Environment-based configs.
        dev/              Configs applied in dev environment.
            params.php    Various parameters used in DI configs.
        prod/             Configs applied in prod environment.
            params.php    Various parameters used in DI configs.
        test/             Configs applied in test environment.
            params.php    Various parameters used in DI configs.
    events.php            Event handlers for both console and web.
    events-console.php    Event handlers for console.
    events-web.php        Event handlers for web.
    params.php            Parameters that are passed to configs.
    providers.php         Service providers for both console and web.
    providers-console.php Service providers for console.
    providers-web.php     Service providers for web.
    routes.php            Defines how URLs are mapped to their handlers.
docs/                     Documentation.
public/                   Files publically accessible from the Internet.
    assets/               Published assets.
    index.php             Entry script.
resources/                Application resources.
    assets/               Asset bundle resources.
    message/              Message translations.
    views/                View templates.
      layout/             View layouts.
runtime/                  Files generated during runtime.
src/                      Application source code.
    Asset/                Asset bundle definitions.
    Command/              Console commands.
    Controller/           Web controller classes.
    Handler/              Custom handler for 404.
    ViewInjection/        Injections that bring additional variables into view templates.
    Installer.php         Additional actions done on Composer commands.
tests/                    A set of Codeception tests for the application.
vendor/                   Installed Composer packages.
configuration.php         Defines how to read application configs.
yii                       Console application entry point.

In general, the files in the application can be divided into two types: those under app/public and those under other directories. The former can be directly accessed via HTTP (i.e., in a browser), while the latter can’t and shouldn’t be.

Each application has an entry script public/index.php which is the only Web accessible PHP script in the application. The entry script is using an application runner to create an instance of an incoming request with the help of one of PSR-7 packages and passes it to an application instance. An application contains a set of middleware that are executed sequentially processing the request. The result is passed further to emitter that takes care of sending a response to the browser.

Depending on the middleware used, the application may behave differently. By default, there is a router that, based on URL requested and configuration, chooses a handler that’s executed to produce a response.

You can learn more about the application template from the yiisoft/app package documentation.

Request Lifecycle

The following diagram shows how an application handles a request.

1. A user makes a request to the entry script public/index.php.
2. The entry script with the help of application runner loads the container configuration and creates an application instance and services necessary to handle the request.
3. Request factory creates a request object based on raw request that came from a user.
4. Application passes a request object through a middleware array configured. One of these is typically a router.
5. The Router finds out what handler to execute based on request and configuration.
6. The handler may load some data, possibly from a database.
7. The handler forms a response by using data. Either directly or with the help of the view package.
8. Emitter receives the response and takes care of sending the response to the user’s browser.