101 lines
2.7 KiB
Markdown
101 lines
2.7 KiB
Markdown
# Placeholder Resolver
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Given a data source representing key => value pairs, resolve placeholders
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like `${foo.bar}` to the value associated with the `foo.bar` key in
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the data source.
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Placeholder Resolver is intended to be used at a relatively low level.
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For example, a configuration library could use Placeholder Resolver
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behind the scenes to allow for configuration values to reference
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other configuration values.
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## Example
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```yml
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conn.driver: mysql
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conn.db_name: example
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conn.hostname: 127.0.0.1
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conn.username: root
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conn.password: pa$$word
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```
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Given the appropriate `DataSourceInterface` implementation to provide
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the above data as a set of key => value pairs, the Placeholder Resolver
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would resolve the value of `$dsnPattern` to `mysql:dbname=example;host=127.0.0.1`.
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```php
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$dsnPattern = '${conn.driver}:dbname=${conn.db_name};host=${conn.hostname}';
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$dsn = $placeholderResolver->resolveValue($dsnPattern);
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// mysql:dbname=example;host=127.0.0.1
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```
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## Requirements
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* PHP 5.3+
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## Usage
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```php
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use Dflydev\PlaceholderResolver\RegexPlaceholderResolver;
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// YourDataSource implements Dflydev\PlaceholderResolver\DataSource\DataSourceInterface
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$dataSource = new YourDataSource;
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// Create the placeholder resolver
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$placeholderResolver = new RegexPlaceholderResolver($dataSource);
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// Start resolving placeholders
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$value = $placeholderResolver->resolvePlaceholder('${foo}');
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```
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The `RegexPlaceholderResolver` constructor accepts two additional arguments,
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a placeholder prefix and a placeholder suffix. The default placeholder
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prefix is `${` and the default placeholder suffix is `}`.
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To handle placeholders that look like `<foo.bar>` instead of `${foo.bar}`,
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one would instantiate the class like this:
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```php
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$placeholderResolver = new RegexPlaceholderResolver($dataSource, '<', '>');
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```
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Placeholders can recursively resolve placeholders. For example, given a
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data source with the following:
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```php
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array(
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'foo' => 'FOO',
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'bar' => 'BAR',
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'FOO.BAR' => 'BAZ!',
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);
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```
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The placeholder `${${foo}.${bar}}` would internally be resolved to
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`${FOO.BAR}` before being further resolved to `BAZ!`.
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Resolved placeholders are cached using the `CacheInterface`. The default
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`Cache` implementation is used unless it is explicitly set on the
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Placeholder Resolver.
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```php
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// YourCache implements Dflydev\PlaceholderResolver\Cache\CacheInterface
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$cache = new YourCache;
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$placeholderResolver->setCache($cache);
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```
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## License
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This library is licensed under the New BSD License - see the LICENSE file
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for details.
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## Community
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If you have questions or want to help out, join us in the
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[#dflydev](irc://irc.freenode.net/#dflydev) channel on irc.freenode.net.
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## Not Invented Here
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Much of the ideas behind this library came from Spring's Property
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Placeholder Configurer implementation.
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