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49 lines
3.4 KiB
Markdown
49 lines
3.4 KiB
Markdown
MVC Overview
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============
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> Note: This chapter is under development.
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Yii implements the model-view-controller (MVC) design pattern, which is
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widely adopted in Web and other application programming. MVC aims to separate business logic from
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user interface considerations, allowing developers to more easily change one component of an application without affecting, or even touching, another.
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In MVC, the *model* represents both the
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information (the data) and the business rules to which the data must adhere. The *view* contains elements
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of the user interface, such as text, images, and form elements. The *controller* manages
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the communication between the model and the view, acting as an agent that handles actions and requests.
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Besides implementing the MVC design pattern, Yii also introduces a *front-controller*, called
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*application*. The front-controller encapsulates the *execution context* for the processing of a request. This means that the front-controller collects information about a user request, and
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then dispatches it to an appropriate controller for the actual handling of that request. In other words, the front-controller is the primary application manager, handling all requests and delegating action accordingly.
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The following diagram shows the static structure of a Yii application:
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A Typical Workflow
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------------------
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The following diagram shows a typical workflow of a Yii application handling a user request:
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1. A user makes a request of the URL `http://www.example.com/index.php?r=post/show&id=1`.
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The Web server handles the request by executing the bootstrap script `index.php`.
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2. The bootstrap script creates an [[yii\web\Application|Application]] instance and runs it.
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3. The Application instance obtains the detailed user request information from an application component named `request`.
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4. The application determines which [controller](controller.md) and which action of that controller was requested.
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This is accomplished with the help of an application component named `urlManager`.
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For this example, the controller is `post`, which refers to the `PostController` class, and the action is `show`,
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whose actual meaning is determined by the controller.
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5. The application creates an instance of the requested controller to further handle the user's request.
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The controller determines that the action `show` refers to a method named `actionShow` in the controller class.
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The controller then creates and executes any filters associated with this action (e.g. access control or benchmarking).
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The action is then executed, if execution is allowed by the filters (e.g., if the user has permission to execute that action).
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6. The action creates a `Post` [model](model.md) instance, using the underlying database table, where the ID value of the corresponding record is `1`.
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7. The action renders a [view](view.md) named `show`, providing to the view the `Post` model instance.
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8. The view reads the attributes of the `Post` model instance and displays the values of those attributes.
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9. The view executes some [widgets](view.md#widgets).
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10. The view rendering result--the output from the previous steps--is embedded within a [layout](view.md#layout) to create a complete HTML page.
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11. The action completes the view rendering and displays the result to the user.
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