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:

namespace Acme\DatabaseConfiguration;

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

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

        // ... add node definitions to the root of the tree
        // $treeBuilder->getRootNode()->...

        return $treeBuilder;
    }
}

Adding Node Definitions to the Tree

Variable Nodes

A tree contains node definitions which can be laid out in a semantic way. This means, using indentation and the fluent notation, it is possible to reflect the real structure of the configuration values:

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

The root node itself is an array node, and has children, like the boolean node auto_connect and the scalar node default_connection. In general: after defining a node, a call to end() takes you one step up in the hierarchy.

Node Type

It is possible to validate the type of a provided value by using the appropriate node definition. Node types are available for:

  • scalar (generic type that includes booleans, strings, integers, floats and null)
  • boolean
  • integer
  • float
  • enum (similar to scalar, but it only allows a finite set of values)
  • array
  • variable (no validation)

and are created with node($name, $type) or their associated shortcut xxxxNode($name) method.

Numeric Node Constraints

Numeric nodes (float and integer) provide two extra constraints - min() and max() - allowing to validate the value:

$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()
;

Enum Nodes

Enum nodes provide a constraint to match the given input against a set of values:

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

This will restrict the delivery options to be either standard, expedited or priority.

Array Nodes

It is possible to add a deeper level to the hierarchy, by adding an array node. The array node itself, may have a pre-defined set of variable nodes:

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

Or you may define a prototype for each node inside an array node:

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

A prototype can be used to add a definition which may be repeated many times inside the current node. According to the prototype definition in the example above, it is possible to have multiple connection arrays (containing a driver, host, etc.).

Sometimes, to improve the user experience of your application or bundle, you may allow to use a simple string or numeric value where an array value is required. Use the castToArray() helper to turn those variables into arrays:

->arrayNode('hosts')
    ->beforeNormalization()->castToArray()->end()
    // ...
->end()

Array Node Options

Before defining the children of an array node, you can provide options like:

useAttributeAsKey()
Provide the name of a child node, whose value should be used as the key in the resulting array. This method also defines the way config array keys are treated, as explained in the following example.
requiresAtLeastOneElement()
There should be at least one element in the array (works only when isRequired() is also called).
addDefaultsIfNotSet()
If any child nodes have default values, use them if explicit values haven’t been provided.
normalizeKeys(false)
If called (with false), keys with dashes are not normalized to underscores. It is recommended to use this with prototype nodes where the user will define a key-value map, to avoid an unnecessary transformation.
ignoreExtraKeys()
Allows extra config keys to be specified under an array without throwing an exception.

A basic prototyped array configuration can be defined as follows:

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

When using the following YAML configuration:

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drivers: ['mysql', 'sqlite']

Or the following XML configuration:

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

The processed configuration is:

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

A more complex example would be to define a prototyped array with children:

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

When using the following YAML configuration:

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

Or the following XML configuration:

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

The processed configuration is:

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

The previous output matches the expected result. However, given the configuration tree, when using the following YAML configuration:

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

The output configuration will be exactly the same as before. In other words, the sf_connection and default configuration keys are lost. The reason is that the Symfony Config component treats arrays as lists by default.

Note

As of writing this, there is an inconsistency: if only one file provides the configuration in question, the keys (i.e. sf_connection and default) are not lost. But if more than one file provides the configuration, the keys are lost as described above.

In order to maintain the array keys use the useAttributeAsKey() method:

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

Note

In YAML, the 'name' argument of useAttributeAsKey() has a special meaning and refers to the key of the map (sf_connection and default in this example). If a child node was defined for the connections node with the key name, then that key of the map would be lost.

The argument of this method (name in the example above) defines the name of the attribute added to each XML node to differentiate them. Now you can use the same YAML configuration shown before or the following XML configuration:

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

In both cases, the processed configuration maintains the sf_connection and default keys:

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 *.

The following example shows these methods in practice:

$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()
;

Deprecating the Option

New in version 5.1: The signature of the setDeprecated() method changed from setDeprecated(?string $message) to setDeprecated(string $package, string $version, ?string $message) in Symfony 5.1.

You can deprecate options using the setDeprecated() method:

$rootNode
    ->children()
        ->integerNode('old_option')
            // this outputs the following generic deprecation message:
            // Since acme/package 1.2: The child node "old_option" at path "..." is deprecated.
            ->setDeprecated('acme/package', '1.2')

            // you can also pass a custom deprecation message (%node% and %path% placeholders are available):
            ->setDeprecated(
                'acme/package',
                '1.2',
                'The "%node%" option is deprecated. Use "new_config_option" instead.'
            )
        ->end()
    ->end()
;

If you use the Web Debug Toolbar, these deprecation notices are shown when the configuration is rebuilt.

Documenting the Option

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

$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:

$arrayNode
    ->canBeEnabled()
;

// is equivalent to

$arrayNode
    ->treatFalseLike(['enabled' => false])
    ->treatTrueLike(['enabled' => true])
    ->treatNullLike(['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():

public function getConfigTreeBuilder()
{
    $treeBuilder = new TreeBuilder('database');

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

    return $treeBuilder;
}

public function addParametersNode()
{
    $treeBuilder = new TreeBuilder('parameters');

    $node = $treeBuilder->getRootNode()
        ->isRequired()
        ->requiresAtLeastOneElement()
        ->useAttributeAsKey('name')
        ->arrayPrototype()
            ->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:

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

            # Prototype
            name:
                value:                ~ # Required
  • XML
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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.

Caution

The target key will not be altered if it’s mixed like foo-bar_moo or if it already exists.

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():

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

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

$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:

$rootNode
    ->children()
        ->arrayNode('connection')
            ->beforeNormalization()
                ->ifString()
                ->then(function ($v) { return ['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:

$rootNode
    ->children()
        ->arrayNode('connection')
            ->children()
                ->scalarNode('driver')
                    ->isRequired()
                    ->validate()
                        ->ifNotInArray(['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()
  • ifEmpty() (since Symfony 3.2)
  • 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.

Configuring the Node Path Separator

Consider the following config builder example:

$treeBuilder = new TreeBuilder('database');

$treeBuilder->getRootNode()
    ->children()
        ->arrayNode('connection')
            ->children()
                ->scalarNode('driver')->end()
            ->end()
        ->end()
    ->end()
;

By default, the hierarchy of nodes in a config path is defined with a dot character (.):

// ...

$node = $treeBuilder->buildTree();
$children = $node->getChildren();
$path = $children['driver']->getPath();
// $path = 'database.connection.driver'

Use the setPathSeparator() method on the config builder to change the path separator:

// ...

$treeBuilder->setPathSeparator('/');
$node = $treeBuilder->buildTree();
$children = $node->getChildren();
$path = $children['driver']->getPath();
// $path = 'database/connection/driver'

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:

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

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

$configs = [$config, $extraConfig];

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