Upgrading from Version 2.0

If you haven’t used Yii2, you can skip this section and get directly to “getting started” section.

While sharing some common ideas and values, Yii 3 is conceptually different from Yii 2. There is no easy upgrade path, so first check maintenance policy and end of life dates for Yii 2 and consider starting new projects on Yii 3 while keeping existing ones on Yii 2.

PHP requirements

Yii3 requires PHP 8.0 or above. As a result, there are language features used that weren’t used in Yii 2:

• Type declarations
• Return type declarations
• Class constant visibility
• Anonymous classes
• ::class
• Generators
• Variadic functions

Preliminary refactoring

It’s a good idea to refactor your Yii 2 project before porting it to Yii 3. That would both make porting easier and benefit the project in question while it’s not moved to Yii 3 yet.

Use DI instead of service locator

Since Yii 3 is forcing you to inject dependencies, it’s a good idea to prepare and switch from using service locator (Yii::$app->) to DI container.

If usage of DI container is problematic for whatever reason, consider moving all calls to Yii::$app-> to controller actions and widgets and passing dependencies manually from a controller to what needs them.

See Dependency injection and container for an explanation of the idea.

Introduce repositories for getting data

Since Active Record isn’t the only way to work with a database in Yii 3, consider introducing repositories that would hide details of getting data and gather them in a single place you can later re-do:

class PostRepository
{
    public function getArchive()
    {
        // ...
    }
    
    public function getTop10ForFrontPage()
    {
        // ...
    }

}

Separate domain layer from infrastructure

In case you have a rich complicated domain, it’s a good idea to separate it from infrastructure provided by framework that’s all the business logic has to go to framework-independent classes.

Move more into components

Yii 3 services are conceptually similar to Yii 2 components, so it’s a good idea to move reusable parts of your application into components.