Upgrading Yii 1 web applications to Yii 2
A guide to migrating PHP web applications from Yii 1 to Yii 2, covering the differences between versions and upgrade strategies.
Yii is a PHP framework ideal for building web applications, APIs and complex dynamic websites.
Version 2 of Yii was released in 2014, whilst the previous major version 1 is scheduled to reach end-of-life in December 2020. Migrating from Yii 1 to Yii 2 remains important for owners of legacy Yii 1 websites.
What's the difference between Yii 1 and Yii 2?
Yii 1 was released in 2008 and quickly established itself as a powerful MVC framework and a viable alternative to other PHP frameworks like CodeIgniter and later, Laravel. Version 1 of Yii had drawbacks though, such as poor environment config support, and the framework often needed a bit of wrapper code to get it to do what you wanted.
Yii 2 was released in 2014 as a completely re-written PHP framework which brought the framework up-to-date with new versions of PHP and resolved almost all of the previous version's shortcomings. Yii 2 makes better use of Composer to manage its own framework code, and 3rd-party packages, and introduces a raft of other improvements to application architecture, configuration and command line support. Migrating from Yii 1 to Yii 2 can therefore bring these benefits to your website or web application.
The developers of Yii announced in 2015 that Yii 1 would be deprecated, and Yii 1 is scheduled to reach end-of-life on 31 December 2020.
What can I do if I have a Yii 1 web application?
Many applications and websites built with Yii 1 still exist and will continue to function. However business owners who use Yii 1 to power their PHP web applications or website should consider upgrading to Yii 2 (or a modern alternative like Laravel) to ensure ongoing security standards and maintainability.
Upgrading from Yii 1 to Yii 2 can be a complex task, as the framework is not backwards compatible - Yii 2 was designed from the ground up in a very different way. However upgrading from Yii 1 is perfectly possible and can often be a good opportunity to redesign and improve aspects of your software.
Upgrading websites and web applications to Yii 2 brings benefits to security, speed and maintainability of the software concerned.
For developers, the Yii website offers very good documentation on upgrading from Yii 1 to Yii 2.