Defining and Processing Configuration Values

Validating Configuration Values

After loading configuration values from all kinds of resources, the values and their structure can be validated using the "Definition" part of the Config Component. Configuration values are usually expected to show some kind of hierarchy. Also, values should be of a certain type, be restricted in number or be one of a given set of values. For example, the following configuration (in YAML) shows a clear hierarchy and some validation rules that should be applied to it (like: "the value for auto_connect must be a boolean value"):

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database:
    auto_connect: true
    default_connection: mysql
    connections:
        mysql:
            host:     localhost
            driver:   mysql
            username: user
            password: pass
        sqlite:
            host:     localhost
            driver:   sqlite
            memory:   true
            username: user
            password: pass

When loading multiple configuration files, it should be possible to merge and overwrite some values. Other values should not be merged and stay as they are when first encountered. Also, some keys are only available when another key has a specific value (in the sample configuration above: the memory key only makes sense when the driver is sqlite).

Defining a Hierarchy of Configuration Values Using the TreeBuilder

All the rules concerning configuration values can be defined using the TreeBuilder.

A TreeBuilder instance should be returned from a custom Configuration class which implements the ConfigurationInterface:

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namespace Acme\DatabaseConfiguration;

use Symfony\Component\Config\Definition\ConfigurationInterface;
use Symfony\Component\Config\Definition\Builder\TreeBuilder;

class DatabaseConfiguration implements ConfigurationInterface
{
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new TreeBuilder();
        $rootNode = $treeBuilder->root('database');

        // ... add node definitions to the root of the tree

        return $treeBuilder;
    }
}

Adding Node Definitions to the Tree

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$rootNode
    ->children()
        ->booleanNode('auto_connect')
            ->defaultTrue()
        ->end()
        ->scalarNode('default_connection')
            ->defaultValue('default')
        ->end()
    ->end()
;

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$rootNode
    ->children()
        ->integerNode('positive_value')
            ->min(0)
        ->end()
        ->floatNode('big_value')
            ->max(5E45)
        ->end()
        ->integerNode('value_inside_a_range')
            ->min(-50)->max(50)
        ->end()
    ->end()
;

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$rootNode
    ->children()
        ->enumNode('delivery')
            ->values(array('standard', 'expedited', 'priority'))
        ->end()
    ->end()
;

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$rootNode
    ->children()
        ->arrayNode('connection')
            ->children()
                ->scalarNode('driver')->end()
                ->scalarNode('host')->end()
                ->scalarNode('username')->end()
                ->scalarNode('password')->end()
            ->end()
        ->end()
    ->end()
;

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$rootNode
    ->children()
        ->arrayNode('connections')
            ->prototype('array')
                ->children()
                    ->scalarNode('driver')->end()
                    ->scalarNode('host')->end()
                    ->scalarNode('username')->end()
                    ->scalarNode('password')->end()
                ->end()
            ->end()
        ->end()
    ->end()
;

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$node
    ->fixXmlConfig('driver')
    ->children()
        ->arrayNode('drivers')
            ->prototype('scalar')->end()
        ->end()
    ->end()
;

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drivers: ['mysql', 'sqlite']

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<driver>mysql</driver>
<driver>sqlite</driver>

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Array(
    [0] => 'mysql'
    [1] => 'sqlite'
)

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$node
    ->fixXmlConfig('connection')
    ->children()
        ->arrayNode('connections')
            ->prototype('array')
                ->children()
                    ->scalarNode('table')->end()
                    ->scalarNode('user')->end()
                    ->scalarNode('password')->end()
                ->end()
            ->end()
        ->end()
    ->end()
;

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connections:
    - { table: symfony, user: root, password: ~ }
    - { table: foo, user: root, password: pa$$ }

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<connection table="symfony" user="root" password="null" />
<connection table="foo" user="root" password="pa$$" />

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Array(
    [0] => Array(
        [table] => 'symfony'
        [user] => 'root'
        [password] => null
    )
    [1] => Array(
        [table] => 'foo'
        [user] => 'root'
        [password] => 'pa$$'
    )
)

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connections:
    sf_connection:
        table: symfony
        user: root
        password: ~
    default:
        table: foo
        user: root
        password: pa$$

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$node
    ->fixXmlConfig('connection')
    ->children()
        ->arrayNode('connections')
            ->useAttributeAsKey('name')
            ->prototype('array')
                ->children()
                    ->scalarNode('table')->end()
                    ->scalarNode('user')->end()
                    ->scalarNode('password')->end()
                ->end()
            ->end()
        ->end()
    ->end()
;

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<connection name="sf_connection"
    table="symfony" user="root" password="null" />
<connection name="default"
    table="foo" user="root" password="pa$$" />

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Array(
    [sf_connection] => Array(
        [table] => 'symfony'
        [user] => 'root'
        [password] => null
    )
    [default] => Array(
        [table] => 'foo'
        [user] => 'root'
        [password] => 'pa$$'
    )
)

Default and Required Values

For all node types, it is possible to define default values and replacement values in case a node has a certain value:

defaultValue()

Set a default value

isRequired()

Must be defined (but may be empty)

cannotBeEmpty()

May not contain an empty value

default*()

(null, true, false), shortcut for defaultValue()

treat*Like()

(null, true, false), provide a replacement value in case the value is *.

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$rootNode
    ->children()
        ->arrayNode('connection')
            ->children()
                ->scalarNode('driver')
                    ->isRequired()
                    ->cannotBeEmpty()
                ->end()
                ->scalarNode('host')
                    ->defaultValue('localhost')
                ->end()
                ->scalarNode('username')->end()
                ->scalarNode('password')->end()
                ->booleanNode('memory')
                    ->defaultFalse()
                ->end()
            ->end()
        ->end()
        ->arrayNode('settings')
            ->addDefaultsIfNotSet()
            ->children()
                ->scalarNode('name')
                    ->isRequired()
                    ->cannotBeEmpty()
                    ->defaultValue('value')
                ->end()
            ->end()
        ->end()
    ->end()
;

Documenting the Option

All options can be documented using the info() method:

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$rootNode
    ->children()
        ->integerNode('entries_per_page')
            ->info('This value is only used for the search results page.')
            ->defaultValue(25)
        ->end()
    ->end()
;

The info will be printed as a comment when dumping the configuration tree with the config:dump-reference command.

In YAML you may have:

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# This value is only used for the search results page.
entries_per_page:     25

and in XML:

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<!-- entries-per-page: This value is only used for the search results page. -->
<config entries-per-page="25" />

Optional Sections

If you have entire sections which are optional and can be enabled/disabled, you can take advantage of the shortcut canBeEnabled() and canBeDisabled() methods:

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$arrayNode
    ->canBeEnabled()
;

// is equivalent to

$arrayNode
    ->treatFalseLike(array('enabled' => false))
    ->treatTrueLike(array('enabled' => true))
    ->treatNullLike(array('enabled' => true))
    ->children()
        ->booleanNode('enabled')
            ->defaultFalse()
;

The canBeDisabled() method looks about the same except that the section would be enabled by default.

Merging Options

Extra options concerning the merge process may be provided. For arrays:

performNoDeepMerging()

When the value is also defined in a second configuration array, don't try to merge an array, but overwrite it entirely

For all nodes:

cannotBeOverwritten()

don't let other configuration arrays overwrite an existing value for this node

Appending Sections

If you have a complex configuration to validate then the tree can grow to be large and you may want to split it up into sections. You can do this by making a section a separate node and then appending it into the main tree with append():

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public function getConfigTreeBuilder()
{
    $treeBuilder = new TreeBuilder();
    $rootNode = $treeBuilder->root('database');

    $rootNode
        ->children()
            ->arrayNode('connection')
                ->children()
                    ->scalarNode('driver')
                        ->isRequired()
                        ->cannotBeEmpty()
                    ->end()
                    ->scalarNode('host')
                        ->defaultValue('localhost')
                    ->end()
                    ->scalarNode('username')->end()
                    ->scalarNode('password')->end()
                    ->booleanNode('memory')
                        ->defaultFalse()
                    ->end()
                ->end()
                ->append($this->addParametersNode())
            ->end()
        ->end()
    ;

    return $treeBuilder;
}

public function addParametersNode()
{
    $treeBuilder = new TreeBuilder();
    $node = $treeBuilder->root('parameters');

    $node
        ->isRequired()
        ->requiresAtLeastOneElement()
        ->useAttributeAsKey('name')
        ->prototype('array')
            ->children()
                ->scalarNode('value')->isRequired()->end()
            ->end()
        ->end()
    ;

    return $node;
}

This is also useful to help you avoid repeating yourself if you have sections of the config that are repeated in different places.

The example results in the following:

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database:
    connection:
        driver:               ~ # Required
        host:                 localhost
        username:             ~
        password:             ~
        memory:               false
        parameters:           # Required

            # Prototype
            name:
                value:                ~ # Required

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<database>
    <!-- driver: Required -->
    <connection
        driver=""
        host="localhost"
        username=""
        password=""
        memory="false"
    >

        <!-- prototype -->
        <!-- value: Required -->
        <parameters
            name="parameters name"
            value=""
        />

    </connection>
</database>

Normalization

When the config files are processed they are first normalized, then merged and finally the tree is used to validate the resulting array. The normalization process is used to remove some of the differences that result from different configuration formats, mainly the differences between YAML and XML.

The separator used in keys is typically _ in YAML and - in XML. For example, auto_connect in YAML and auto-connect in XML. The normalization would make both of these auto_connect.

Another difference between YAML and XML is in the way arrays of values may be represented. In YAML you may have:

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twig:
    extensions: ['twig.extension.foo', 'twig.extension.bar']

and in XML:

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<twig:config>
    <twig:extension>twig.extension.foo</twig:extension>
    <twig:extension>twig.extension.bar</twig:extension>
</twig:config>

This difference can be removed in normalization by pluralizing the key used in XML. You can specify that you want a key to be pluralized in this way with fixXmlConfig():

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$rootNode
    ->fixXmlConfig('extension')
    ->children()
        ->arrayNode('extensions')
            ->prototype('scalar')->end()
        ->end()
    ->end()
;

If it is an irregular pluralization you can specify the plural to use as a second argument:

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$rootNode
    ->fixXmlConfig('child', 'children')
    ->children()
        ->arrayNode('children')
            // ...
        ->end()
    ->end()
;

As well as fixing this, fixXmlConfig() ensures that single XML elements are still turned into an array. So you may have:

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<connection>default</connection>
<connection>extra</connection>

and sometimes only:

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<connection>default</connection>

By default connection would be an array in the first case and a string in the second making it difficult to validate. You can ensure it is always an array with fixXmlConfig().

You can further control the normalization process if you need to. For example, you may want to allow a string to be set and used as a particular key or several keys to be set explicitly. So that, if everything apart from name is optional in this config:

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connection:
    name:     my_mysql_connection
    host:     localhost
    driver:   mysql
    username: user
    password: pass

you can allow the following as well:

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connection: my_mysql_connection

By changing a string value into an associative array with name as the key:

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$rootNode
    ->children()
        ->arrayNode('connection')
            ->beforeNormalization()
                ->ifString()
                ->then(function ($v) { return array('name' => $v); })
            ->end()
            ->children()
                ->scalarNode('name')->isRequired()
                // ...
            ->end()
        ->end()
    ->end()
;

Validation Rules

More advanced validation rules can be provided using the ExprBuilder. This builder implements a fluent interface for a well-known control structure. The builder is used for adding advanced validation rules to node definitions, like:

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$rootNode
    ->children()
        ->arrayNode('connection')
            ->children()
                ->scalarNode('driver')
                    ->isRequired()
                    ->validate()
                        ->ifNotInArray(array('mysql', 'sqlite', 'mssql'))
                        ->thenInvalid('Invalid database driver %s')
                    ->end()
                ->end()
            ->end()
        ->end()
    ->end()
;

A validation rule always has an "if" part. You can specify this part in the following ways:

• ifTrue()
• ifString()
• ifNull()
• ifArray()
• ifInArray()
• ifNotInArray()
• always()

A validation rule also requires a "then" part:

• then()
• thenEmptyArray()
• thenInvalid()
• thenUnset()

Usually, "then" is a closure. Its return value will be used as a new value for the node, instead of the node's original value.

Processing Configuration Values

The Processor uses the tree as it was built using the TreeBuilder to process multiple arrays of configuration values that should be merged. If any value is not of the expected type, is mandatory and yet undefined, or could not be validated in some other way, an exception will be thrown. Otherwise the result is a clean array of configuration values:

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use Symfony\Component\Yaml\Yaml;
use Symfony\Component\Config\Definition\Processor;
use Acme\DatabaseConfiguration;

$config = Yaml::parse(
    file_get_contents(__DIR__.'/src/Matthias/config/config.yml')
);
$extraConfig = Yaml::parse(
    file_get_contents(__DIR__.'/src/Matthias/config/config_extra.yml')
);

$configs = array($config, $extraConfig);

$processor = new Processor();
$databaseConfiguration = new DatabaseConfiguration();
$processedConfiguration = $processor->processConfiguration(
    $databaseConfiguration,
    $configs
);