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Hydrator Configuration

Even deveopers who have used Doctrine or an ORM a lot may not have experience with hydrators. This section is to educate and help the developer understand hydrators and how to use them in relation to Doctrine ORM and GraphQL.

A hydrator moves data into and out of an object as an array. The array may contain scalar values, arrays, and closures. For instance, if you have an entity with the fields:


a hydrator can create an array from your entity resulting in:


The Zend Framework documentaion on Hydrators is a good read for background about coding hydrators from scratch.

The Doctrine Hydrator documentation is more complete and more pertinent to this repository. A notable section is By Value and By Reference

Generating a Skeleton Configuration

This module uses hydrators to extract data from the Doctrine entities. You can configure multiple sections of hydrators so one permissioned user may receive different data than a different permission or one query to an entity may return different fields than another query to the same entity.

Because creating hydrator configurations for every section for every entity in your object manager(s) is tedious this module provides an auto-generating configuration tool.

To generate configuration:

php public/index.php graphql:config-skeleton [--hydrator-sections=] [--object-manager=]

The hydrator-sections parameter is a comma delimited list of sections to generate such as default,admin.

The object-manager parameter is optional and defaults to doctrine.entitymanager.orm_default. For each object manager you want to serve data with in your application create a configuration using this tool. The tool outputs a configuration file. Write the file to your project root location then move it to your config/autoload directory.

php public/index.php graphql:config-skeleton >
mv config/autoload

(Writing directly into the config/autoload directory is not recommended at run time.)

Default hydrator strategies and filters are set for every association and field in your ORM. Modify each hydrator configuration section with your hydrator strategies and hydrator filters as needed.

Generated Configuration

Here is an example of a generated configuration:

'ZF\\Doctrine\\GraphQL\\Hydrator\\ZF_Doctrine_Audit_Entity_Revision' => [
    'default' => [
        'entity_class' => \ZF\Doctrine\Audit\Entity\Revision::class,
        'object_manager' => 'doctrine.entitymanager.orm_zf_doctrine_audit',
        'by_value' => true,
        'use_generated_hydrator' => true,
        'naming_strategy' => null,
        'hydrator' => null,
        'strategies' => [
            'id' => \ZF\Doctrine\GraphQL\Hydrator\Strategy\ToInteger::class,
            'comment' => \ZF\Doctrine\GraphQL\Hydrator\Strategy\FieldDefault::class,
            'connectionId' => \ZF\Doctrine\GraphQL\Hydrator\Strategy\ToInteger::class,
            'createdAt' => \ZF\Doctrine\GraphQL\Hydrator\Strategy\FieldDefault::class,
            'userEmail' => \ZF\Doctrine\GraphQL\Hydrator\Strategy\FieldDefault::class,
            'userId' => \ZF\Doctrine\GraphQL\Hydrator\Strategy\ToInteger::class,
            'userName' => \ZF\Doctrine\GraphQL\Hydrator\Strategy\FieldDefault::class,
            'revisionEntity' => \ZF\Doctrine\GraphQL\Hydrator\Strategy\AssociationDefault::class,
        'filters' => [
            'default' => [
                'condition' => 'and',
                'filter' => \ZF\Doctrine\GraphQL\Hydrator\Filter\FilterDefault::class,
        'documentation' => [
            '_entity' => '',
            'id' => '',
            'comment' => '',
            'connectionId' => '',
            'createdAt' => '',
            'userEmail' => '',
            'userId' => '',
            'userName' => '',

The entity_class is the fully qualified entity class name this configuration section is for.

The object_manager is the service manager alias for the object manager which manages the entity_class.

by_value is an important switch. When set to true the values for the entity will be fetched using their getter methods such as getName() for a name field. When set to false the entity will be Reflected and the property value of the entity class will be extracte by reference. If your entities are not extracting properly try toggling this value.

by_value set to false is useful when your entity does not have getter methods such as a dynamically created entity. API-Skeletons/zf-doctrine-audit is a good example for this. The dynamically generated auditing entities do not have getter methods but do have properties to contain the field values. These can be extracted by reference.

use_generated_hydrator is usually set to true. Because GraphQL uses hydrators for extraction only this value is not used. But if you want to use the same configured hydrators to hydrate an entity please see the code for its use.

hydrator allows complete overriding of the extract service. If set the extract and hydrate services will be assigned to the specified hydrator.

naming_strategy is an instance of ZendHydratorNamingStrategyNamingStrategyInterface and is a service manager alias. You may only have one naming_strategy per hydrator configuration. A naming strategy lets you rename fields.

strategies are quite important for extracting entities. These can change the extracted value in whatever way you wish such as rot13() email addresses. They can return an empty value but for that case it's better to filter out the field completely.

filters are toggle switches for fields. If you return false for a field name it will remove the field from the extract result.

documentation section is for fields only. Relations are not documented because that is not supported by GraphiQL. Use this section to document each field and the entity. The reserved name _entity contains the documentation for the entity.


There are some hydrator stragegies included with this module. In GraphQL types are very important and this module introspects your ORM metadata to correctly type against GraphQL types. By default integer, float, and boolean fields are automatically assigned to the correct hydrator strategy.

Many to Many Owning Side Relationships

{ artist { user { role { user { name } } } } }

This query would return all user names who share the same role permissions as the user who created the artist. To prevent this the graphql:config-skeleton command nullifies the owning side of many to many relations by default causing an error when the query tries to go from role > user but not when it goes from user > role becuase role is the owning side of the many to many relationship. See NullifyOwningAssociation for more information.

Documenting Entities

Introspection of entities is a core component to GraphQL. The introspection allows you to document your types. Because entities are types there is a section inside each hydrator configuration for documenting your entity and fields through introspection.

'documentation' => [
    '_entity' => 'The Artist entity contains bands, groups, and individual performers.',
    'id' => 'Primary Key for the Artist',
    'abbreviation' => 'An abbreviation for the Artist',
    'createdAt' => 'DateTime the Artist record was created',
    'description' => 'A description of the Artist',
    'icon' => 'The Artist icon',
    'name' => 'The name of the performer.',

There is one special field, _entity which is the description for the entity itself. The rest of the fields describe documentation for each field.

Documentation is specific to each hydrator section allowing you to describe the same entity in different ways. The Documentation will be returned in tools like GraphiQL

GraphiQL is the standard for browsing introspected GraphQL types. zf-doctrine-graphql fully supports GraphiQL.