yii2/docs/guide/start-workflow.md

Running Applications

You now have a working Yii application which can be accessed via URL http://hostname/index.php. In this section, we will introduce what functionalities this application has, how the code is organized, and how the application handles requests in general.

Info: For simplicity, throughout this "Getting Started" tutorial we assume that you have set basic/web as the document root of your Web server. If you have not done so, the URL for accessing your application could be http://hostname/basic/web/index.php, or something similar. Please adjust the URLs accordingly in our descriptions.

Functionalities

The application that you have installed contains four pages:

• the homepage is the page displayed when you access the URL http://hostname/index.php;
• the "About" page;
• the "Contact" page displays a contact form that allows end users to contact you by filling out the form;
• the "Login" page displays a login form that can be used to authenticate end users. Try logging in with "admin/admin", and you will find the "Login" main menu item will change to "Logout".

These pages share a common header and footer. The header contains a main menu bar to allow navigate among different pages.

You should also see a toolbar sticking at the bottom of the browser window when it displays any of the above pages. This is a useful debugger tool provided by Yii to help you check various debugging information about the application execution, such as log messages, response status, database queries, and so on.

Application Structure

The following is a list of the most important directories and files in your application,

basic/                  application base path
    composer.json       used by Composer, describes package information
    config/             contains application and other configurations
        console.php     the console application configuration
        web.php         the Web application configuration
    commands/           contains console command classes
    controllers/        contains controller classes
    models/             contains model classes
    runtime/            contains files generated by Yii during runtime, such as logs, cache files
    vendor/             contains the installed Composer packages, including the Yii framework
    views/              contains view files
    web/                application Web root, contains Web accessible files
        assets/         contains published asset files (js, css) by Yii
        index.php       the entry script of the application
    yii                 the Yii console command execution script

In general, the files in the application can be divided into two parts: those under basic/web and those under other directories. The former can be directly accessed from Web, while the latter can not and should not.

Yii implements the model-view-controller (MVC) design pattern which is reflected in the above directory organization. The models directory contains all model classes, the views directory contains all view scripts, and the controllers directory contains all controller classes.

The following diagram shows the static structure of an application.

Each application has an entry script web/index.php which is the only Web accessible PHP script in the application. The entry script takes an incoming request and creates an application instance to handle it. The application resolves the request with the help of its components and dispatches the request to MVC. Widgets are used in the views to help build complex and dynamic user interface elements.

Request Lifecycle

The following diagram shows how an application handles a request.

1. A user makes a request to the entry script web/index.php.
2. The entry script loads the application configuration and creates an application instance to handle the request.
3. The application resolves the requested route with the help of the request application component.
4. The application creates a controller instance to handle the request.
5. The controller creates an action instance and performs the filters for the action.
6. If any filter fails, the action is cancelled.
7. If all filters pass, the action is being executed.
8. The action loads a data model, possibly from a database.
9. The action renders a view with the data model.
10. The rendering result is to the response application component.
11. The response component sends the rendering result to the user.