MVC Overview
Yii implements the model-view-controller (MVC) design pattern, which is widely adopted in Web programming. MVC aims to separate business logic from user interface considerations, so that developers can more easily change each part without affecting the other. In MVC, the model represents the information (the data) and the business rules; the view contains elements of the user interface such as text, form inputs; and the controller manages the communication between the model and the view.
Besides implementing MVC, Yii also introduces a front-controller, called
Application
, which encapsulates the execution context for the processing
of a request. Application collects information about a user request and
then dispatches it to an appropriate controller for further handling.
The following diagram shows the static structure of a Yii application:
A Typical Workflow
The following diagram shows a typical workflow of a Yii application when it is handling a user request:
- A user makes a request with the URL
http://www.example.com/index.php?r=post/show&id=1
and the Web server handles the request by executing the bootstrap scriptindex.php
. - The bootstrap script creates an Application instance and runs it.
- The Application obtains detailed user request information from
an application component
named
request
. - The application determines the requested controller
and action with the help
of an application component named
urlManager
. For this example, the controller ispost
, which refers to thePostController
class; and the action isshow
, whose actual meaning is determined by the controller. - The application creates an instance of the requested controller
to further handle the user request. The controller determines that the action
show
refers to a method namedactionShow
in the controller class. It then creates and executes filters (e.g. access control, benchmarking) associated with this action. The action is executed if it is allowed by the filters. - The action reads a
Post
model whose ID is1
from the database. - The action renders a view named
show
with thePost
model. - The view reads and displays the attributes of the
Post
model. - The view executes some widgets.
- The view rendering result is embedded in a layout.
- The action completes the view rendering and displays the result to the user.