(For more resources related to this topic, see here.)

Easy

To run a Yii version 1.x-powered web application, all you need are the core framework files and a web server supporting PHP 5.1.0 or higher. To develop with Yii, you only need to know PHP and object-oriented programming. You are not required to learn any new configuration or templating language. Building a Yii application mainly involves writing and maintaining your own custom PHP classes, some of which will extend from the core, Yii framework component classes.

Yii incorporates many of the great ideas and work from other well-known web programming frameworks and applications. So if you are coming to Yii from using other web development frameworks, it is likely that you will find it familiar and easy to navigate.

Yii also embraces a convention over configuration philosophy, which contributes to its ease of use. This means that Yii has sensible defaults for almost all the aspects that are used for configuring your application. Following the prescribed conventions, you can write less code and spend less time developing your application. However, Yii does not force your hand. It allows you to customize all of its defaults and makes it easy to override all of these conventions.

Efficient

Yii is a high-performance, component-based framework that can be used for developing web applications on any scale. It encourages maximum code reuse in web programming and can significantly accelerate the development process. As mentioned previously, if you stick with Yii’s built-in conventions, you can get your application up and running with little or no manual configuration.

Yii is also designed to help you with DRY development. DRY stands for Don’t Repeat Yourself , a key concept of agile application development. All Yii applications are built using the Model-View-Controller (MVC) architecture. Yiienforces this development pattern by providing a place to keep each piece of your MVC code. This minimizes duplication and helps promote code reuse and ease of maintainability. The less code you need to write, the less time it takes to get your application to market. The easier it is to maintain your application, the longer it will stay on the market.

Of course, the framework is not just efficient to use, it is remarkably fast and performance optimized. Yii has been developed with performance optimization in mind from the very beginning, and the result is one of the most efficient PHP frameworks around. So any additional overhead that Yii adds to applications written on top of it is extremely negligible.

Extensible

Yii has been carefully designed to allow nearly every piece of its code to be extended and customized to meet any project requirement. In fact, it is difficult not to take advantage of Yii’s ease of extensibility, since a primary activity when developing a Yii application is extending the core framework classes. And if you want to turn your extended code into useful tools for other developers, Yii provides easy-to-follow steps and guidelines to help you create such third-party extensions. This allows you to contribute to Yii’s ever-growing list of features and actively participate in extending Yii itself.

Remarkably, this ease-of-use, superior performance, and depth of extensibility does not come at the cost of sacrificing its features. Yii is packed with features to help you meet those high demands placed on today’s web applications. AJAX-enabled widgets, RESTful and SOAP Web services integration, enforcement of an MVC architecture, DAO and relational ActiveRecord database layer, sophisticated caching, hierarchical role-based access control, theming, internationalization (I18N), and localization (L10N) are just the tip of the Yii iceberg. As of version 1.1, the core framework is now packaged with an official extension library called Zii. These extensions are developed and maintained by the core framework team members, and continue to extend Yii’s core feature set. And with a deep community of users who are also contributing by writing Yiiextensions, the overall feature set available to a Yii-powered application is growing daily. A list of available, user-contributed extensions on the Yii framework website can be found at http://www.yiiframework.com/extensions. There is also an unofficial extension repository of great extensions that can be found at http://yiiext.github.com/, which really demonstrates the strength of the community and the extensibility of this framework.

MVC architecture

As mentioned earlier, Yii is an MVC framework and provides an explicit directory structure for each piece of model, view, and controller code. Before we get started with building our first Yii application, we need to define a few key terms and look at how Yii implements and enforces this MVC architecture.

Model

Typically in an MVC architecture, the model is responsible for maintaining the state, and should encapsulate the business rules that apply to the data that defines this state. A model in Yii is any instance of the framework class CModel or its child class. A model class is typically comprised of data attributes that can have separate labels (something user friendly for the purpose of display), and can be validated against a set of rules defined in the model. The data that makes up the attributes in the model class could come from a row of a database table or from the fields in a user input form.

Yii implements two kinds of models, namely the form model (a CFormModel class) and active record (a CActiveRecord class). They both extend from the same base class CModel. The class CFormModel represents a data model that collects HTML form inputs. It encapsulates all the logic for form field validation, and any other business logic that may need to be applied to the form field data. It can then store this data in memory or, with the help of an active record model, store data in a database.

Active Record (AR) is a design pattern used to abstract database access in an objectoriented fashion. Each AR object in Yii is an instance of CActiveRecord or its child class, which wraps a single row in a database table or view, that encapsulates all the logic and details around database access, and houses much of the business logic that is required to be applied to that data. The data field values for each column in the table row are represented as properties of the active record object.

View

Typically the view is responsible for rendering the user interface, often based on the data in the model. A view in Yii is a PHP script that contains user interface-related elements, often built using HTML, but can also contain PHP statements. Usually, any PHP statements within the view are very simple, conditional or looping statements, or refer to other Yii UI-related elements such as HTML helper class methods or prebuilt widgets. More sophisticated logic should be separated from the view and placed appropriately in either the model, if dealing directly with the data, or the controller, for more general business logic.

Controller

The controller is our main director of a routed request, and is responsible for taking user input, interacting with the model, and instructing the view to update and display appropriately. A controller in Yii is an instance of CController or a child class thereof. When a controller runs, it performs the requested action, which then interacts with the necessary models, and renders an appropriate view. An action, in its simplest form, is a controller class method whose name starts with the word action