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132 lines
5.3 KiB
Markdown
132 lines
5.3 KiB
Markdown
Aliases
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=======
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Aliases are used to represent file paths or URLs to avoid hard-coding absolute paths or URLs in your code.
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An alias must start with a `@` character so that it can be differentiated from file paths and URLs.
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For example, the alias `@yii` represents the installation path of the Yii framework, while `@web` represents
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the base URL for the currently running Web application.
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Defining Aliases <a name="defining-aliases"></a>
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----------------
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You can call [[Yii::setAlias()]] to define an alias for a given file path or URL. For example,
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```php
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// an alias of file path
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Yii::setAlias('@foo', '/path/to/foo');
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// an alias of URL
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Yii::setAlias('@bar', 'http://www.example.com');
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```
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> Note: A file path or URL being aliased may NOT necessarily refer to an existing file or resource.
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Given an alias, you may derive a new alias (without the need of calling [[Yii::setAlias()]]) by appending
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a slash `/` followed with one or several path segments. We call the aliases defined via [[Yii::setAlias()]]
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*root aliases*, while the aliases derived from them *derived aliases*. For example, `@foo` is a root alias,
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while `@foo/bar/file.php` is a derived alias.
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You can define an alias using another alias (either root alias or derived alias is fine):
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```php
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Yii::setAlias('@foobar', '@foo/bar');
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```
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Root aliases are usually defined during the [bootstrapping](runtime-bootstrapping.md) stage.
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For example, you may call [[Yii::setAlias()]] in the [entry script](structure-entry-scripts.md).
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For convenience, [Application](structure-applications.md) provides a writable property named `aliases`
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that you can configure in the application [configuration](concept-configurations.md), like the following,
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```php
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return [
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// ...
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'aliases' => [
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'@foo' => '/path/to/foo',
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'@bar' => 'http://www.example.com',
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],
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];
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```
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Resolving Aliases <a name="resolving-aliases"></a>
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-----------------
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You can call [[Yii::getAlias()]] to resolve a root alias into the file path or URL it is representing.
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The same method can also resolve a derived alias into the corresponding file path or URL. For example,
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```php
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echo Yii::getAlias('@foo'); // displays: /path/to/foo
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echo Yii::getAlias('@bar'); // displays: http://www.example.com
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echo Yii::getAlias('@foo/bar/file.php'); // displays: /path/to/foo/bar/file.php
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```
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The path/URL represented by a derived alias is determined by replacing the root alias part with its corresponding
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path/URL in the derived alias.
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> Note: The [[Yii::getAlias()]] method does not check whether the resulting path/URL refers to an existing file or resource.
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A root alias may also contain slash `/` characters. The [[Yii::getAlias()]] method
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is intelligent enough to tell which part of an alias is a root alias and thus correctly determines
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the corresponding file path or URL. For example,
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```php
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Yii::setAlias('@foo', '/path/to/foo');
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Yii::setAlias('@foo/bar', '/path2/bar');
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Yii::getAlias('@foo/test/file.php'); // displays: /path/to/foo/test/file.php
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Yii::getAlias('@foo/bar/file.php'); // displays: /path2/bar/file.php
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```
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If `@foo/bar` is not defined as a root alias, the last statement would display `/path/to/foo/bar/file.php`.
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Using Aliases <a name="using-aliases"></a>
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-------------
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Aliases are recognized in many places in Yii without the need of calling [[Yii::getAlias()]] to convert
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them into paths/URLs. For example, [[yii\caching\FileCache::cachePath]] can accept both a file path
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and an alias representing a file path, thanks to the `@` prefix which allows it to differentiate a file path
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from an alias.
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```php
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use yii\caching\FileCache;
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$cache = new FileCache([
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'cachePath' => '@runtime/cache',
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]);
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```
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Please pay attention to the API documentation to see if a property or method parameter supports aliases.
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Predefined Aliases <a name="predefined-aliases"></a>
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------------------
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Yii predefines a set of aliases to ease the need of referencing commonly used file paths and URLs.
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The following is the list of the predefined aliases:
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- `@yii`: the directory where the `BaseYii.php` file is located (also called the framework directory).
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- `@app`: the [[yii\base\Application::basePath|base path]] of the currently running application.
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- `@runtime`: the [[yii\base\Application::runtimePath|runtime path]] of the currently running application.
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- `@vendor`: the [[yii\base\Application::vendorPath|Composer vendor directory].
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- `@webroot`: the Web root directory of the currently running Web application.
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- `@web`: the base URL of the currently running Web application.
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The `@yii` alias is defined when you include the `Yii.php` file in your [entry script](structure-entry-scripts.md),
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while the rest of the aliases are defined in the application constructor when applying the application
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[configuration](concept-configurations.md).
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Extension Aliases <a name="extension-aliases"></a>
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-----------------
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An alias is automatically defined for each [extension](structure-extensions.md) that is installed via Composer.
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The alias is named after the root namespace of the extension as declared in its `composer.json` file, and it
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represents the root directory of the package. For example, if you install the `yiisoft/yii2-jui` extension,
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you will automatically have the alias `@yii/jui` defined during the [bootstrapping](runtime-bootstrapping.md) stage:
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```php
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Yii::setAlias('@yii/jui', 'VendorPath/yiisoft/yii2-jui');
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```
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