Defining and Processing Configuration Values

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"):

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
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:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
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

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:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
$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 type are available for:

  • scalar
  • boolean
  • integer
  • float
  • enum
  • 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:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
$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:

1
2
3
4
5
6
7
$rootNode
    ->children()
        ->enumNode('gender')
            ->values(array('male', 'female'))
        ->end()
    ->end()
;

This will restrict the gender option to be either male or female.

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:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
$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:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
$rootNode
    ->children()
        ->arrayNode('connections')
            ->prototype('array')
                ->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.).

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.
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.

An example of this:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
$rootNode
    ->children()
        ->arrayNode('parameters')
            ->isRequired()
            ->requiresAtLeastOneElement()
            ->useAttributeAsKey('name')
            ->prototype('array')
                ->children()
                    ->scalarNode('value')->isRequired()->end()
                ->end()
            ->end()
        ->end()
    ->end()
;

In YAML, the configuration might look like this:

1
2
3
database:
    parameters:
        param1: { value: param1val }

In XML, each parameters node would have a name attribute (along with value), which would be removed and used as the key for that element in the final array. The useAttributeAsKey is useful for normalizing how arrays are specified between different formats like XML and YAML.

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 *.
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
$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()
;

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:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
$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():

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
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()
{
    $builder = new TreeBuilder();
    $node = $builder->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.

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:

1
2
twig:
    extensions: ['twig.extension.foo', 'twig.extension.bar']

and in XML:

1
2
3
4
<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():

1
2
3
4
5
6
7
8
$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:

1
2
3
4
5
6
7
8
$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:

1
2
<connection>default</connection>
<connection>extra</connection>

and sometimes only:

1
<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:

1
2
3
4
5
6
connection:
    name:     my_mysql_connection
    host:     localhost
    driver:   mysql
    username: user
    password: pass

you can allow the following as well:

1
connection: my_mysql_connection

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

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
$rootNode
    ->children()
        ->arrayNode('connection')
            ->beforeNormalization()
                ->ifString()
                ->then(function($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:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
$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:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
use Symfony\Component\Yaml\Yaml;
use Symfony\Component\Config\Definition\Processor;
use Acme\DatabaseConfiguration;

$config1 = Yaml::parse(__DIR__.'/src/Matthias/config/config.yml');
$config2 = Yaml::parse(__DIR__.'/src/Matthias/config/config_extra.yml');

$configs = array($config1, $config2);

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

This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License .