yii2/docs/guide/start-lifecycle.md

Request Lifecycle

Note: This chapter is under development.

The following diagram shows a typical workflow of a Yii application handling a user request:

1. A user makes a request of the URL http://www.example.com/index.php?r=post/show&id=1. The Web server handles the request by executing the bootstrap script index.php.
2. The bootstrap script creates an yii\web\Application instance and runs it.
3. The Application instance obtains the detailed user request information from an application component named request.
4. The application determines which controller and which action of that controller was requested. This is accomplished with the help of an application component named urlManager. For this example, the controller is post, which refers to the PostController class, and the action is show, whose actual meaning is determined by the controller.
5. The application creates an instance of the requested controller to further handle the user's request. The controller determines that the action show refers to a method named actionShow in the controller class. The controller then creates and executes any filters associated with this action (e.g. access control or benchmarking). The action is then executed, if execution is allowed by the filters (e.g., if the user has permission to execute that action).
6. The action creates a Post model instance, using the underlying database table, where the ID value of the corresponding record is 1.
7. The action renders a view named show, providing to the view the Post model instance.
8. The view reads the attributes of the Post model instance and displays the values of those attributes.
9. The view executes some widgets.
10. The view rendering result--the output from the previous steps--is embedded within a layout to create a complete HTML page.
11. The action completes the view rendering and displays the result to the user.