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Various Yii 3.0 related documentation

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Aliases

You can use aliases to represent file paths or URLs so that you don’t have to hard-code absolute paths or URLs in your project. An alias must start with the @ character to be differentiated from normal file paths and URLs. Alias defined without leading @ will be prefixed with @ character.

Default Yii application has some aliases pre-defined in config/params.php. For example, the alias @public represents the web root path; @baseUrl represents the base URL for the currently running Web application.

Defining aliases

You can define an alias via application’s config/params.php:

return [
    // ...
    
    'yiisoft/aliases' => [
        'aliases' => [
            // ...
        
            // an alias of a file path
            '@foo' => '/path/to/foo',
        
            // an alias of a URL
            '@bar' => 'https://www.example.com',
        
            // an alias of a concrete file that contains a \foo\Bar class 
            '@foo/Bar.php' => '/definitely/not/foo/Bar.php',
        ],
    ],
];

[!NOTE] The file path or URL being aliased may not necessarily refer to an existing file or resource.

Given a defined alias, you may derive a new alias by appending a slash / followed with one or more path segments. For example, @foo is a root alias, while @foo/bar/file.php is a derived alias.

You can define an alias using another alias (either root or derived):

'@foobar' => '@foo/bar',

The yiisoft/aliases parameter initializes Aliases service from yiisoft/aliases package. You can set extra aliases in runtime by using the service:

use \Yiisoft\Aliases\Aliases;

public function actionIndex(Aliases $aliases)
{
    $aliases->set('@uploads', '@root/uploads');
}

Using aliases in configuration

It’s preferred to resolve aliases at the configuration level, so services get URLs and paths as ready to use strings:

<?php

declare(strict_types=1);

use Yiisoft\Aliases\Aliases;
use Yiisoft\Cache\File\FileCache;

/* @var $params array */

return [
    FileCache::class => static fn (Aliases $aliases) => new FileCache(
        $aliases->get($params['yiisoft/cache-file']['fileCache']['path'])
    ),
];

Resolving aliases

You can use Aliases service to resolve an alias or derived alias into the file path or URL it represents:

use \Yiisoft\Aliases\Aliases;

public function actionIndex(Aliases $aliases)
{
    $foo = $aliases->get('@foo'); // /path/to/foo
    $bar = $aliases->get('@bar'); // https://www.example.com
    $file = $aliases->get('@foo/bar/file.php'); // /path/to/foo/bar/file.php
}

The path/URL represented by a derived alias is determined by replacing the root alias part with its corresponding path/URL in the derived alias.

[!NOTE] The get() method doesn’t check whether the resulting path/URL refers to an existing file or resource.

A root alias may also contain slash / characters. The get() method is intelligent enough to tell, which part of an alias is a root alias and thus correctly determines the corresponding file path or URL:

use \Yiisoft\Aliases\Aliases;

public function actionIndex(Aliases $aliases)
{
    $aliases->set('@foo', '/path/to/foo');
    $aliases->set('@foo/bar', '/path2/bar');

    $aliases->get('@foo/test/file.php'); // /path/to/foo/test/file.php
    $aliases->get('@foo/bar/file.php'); // /path2/bar/file.php
}

If @foo/bar isn’t defined as a root alias, the last statement would display /path/to/foo/bar/file.php.

Predefined aliases

Yii application predefines a set of aliases to reference commonly used file paths and URLs: