Extending the API

Registering Your Resource

You can extend the API to include custom resources. Most resources are correlated to Omeka records, but you may include non-record resources as well. In your plugin class, register your resource using the api_resources filter, following this format:

<?php
protected $_filters = array('api_resources');

public function filterApiResources($apiResources)
{
    // For the resource URI: /api/your_resources/[:id]
    $apiResources['your_resources'] = array(
        // Module associated with your resource.
        'module' => 'your-plugin-name',
        // Controller associated with your resource.
        'controller' => 'your-resource-controller',
        // Type of record associated with your resource.
        'record_type' => 'YourResourceRecord',
        // List of actions available for your resource.
        'actions' => array(
            'index',  // GET request without ID
            'get',    // GET request with ID
            'post',   // POST request
            'put',    // PUT request (ID is required)
            'delete', // DELETE request (ID is required)
        ),
        // List of GET parameters available for your index action.
        'index_params' => array('foo', 'bar'),
    );
    return $apiResources;
}

If not given, module and controller fall back to their defaults, “default” and “api”. Resources using the default controller MUST include a record_type. Remove actions that are not wanted or not implemented. For index actions, all GET parameters must be registered with the index_params whitelist.

Using the Default Controller

If your resource corresponds to an Omeka record, we highly recommend that you use the default controller. Doing so will ensure consistent behavior across resources. These records must extend Omeka_Record_AbstractRecord, implement Zend_Acl_Resource_Interface, and have a corresponding API adapter called Api_{YourRecordType} that must extend Omeka_Record_Api_AbstractRecordAdapter and be saved to your plugin’s models directory in a subdirectory named Api. This adapter is responsible for building representations of, and setting properties to, your record.

For example, an API adapter for YourRecordType saved to YourPlugin/models/Api/YourRecordType.php:

<?php
class Api_YourRecordType extends Omeka_Record_Api_AbstractRecordAdapter
{
    // Get the REST representation of a record.
    public function getRepresentation(Omeka_Record_AbstractRecord $record)
    {
        // Return a PHP array, representing the passed record.
    }

    // Set data to a record during a POST request.
    public function setPostData(Omeka_Record_AbstractRecord $record, $data)
    {
        // Set properties directly to a new record.
    }

    // Set data to a record during a PUT request.
    public function setPutData(Omeka_Record_AbstractRecord $record, $data)
    {
        // Set properties directly to an existing record.
    }
}

Omeka_Record_Api_AbstractRecordAdapter provides a few convenience methods that make representation and record building easier:

  • getResourceUrl($uri): Get the absolute URL to the passed resource. The convention is to provide an absolute URL to all resources in your representations, identified by the “url” key. This follows a hypermedia approach to API design, offering the client an easy way to consume and locate available resources. Note that this is a static method, which means you can use it in your plugin class when extending an existing resource (see “Extending Existing Resources” below).
  • getDate($date): Format a date string as an ISO 8601 date, UTC timezone. The convention is to convert all dates to this format. Note that this is a static method.
  • getElementTextRepresentations($record): Get representations of element texts belonging to a record. The record must initialize the ElementText mixin.
  • setElementTextData($record, $data): Set element text data to a record. The record must initialize the ElementText mixin.

By implementing Zend_Acl_Resource_Interface, you record class must include the getResourceId() method. This identifies your record as relating to a unique ACL resource ID, which is used during permission checks, often automatically.

<?php
public function getResourceId()
{
    // This is typically the name of the plugin, an underscore, and the pluralized record type.
    return 'YourPlugin_YourRecords';
}

You may find this resource ID already defined in the plugin’s define_acl hook. If not you’ll need to add it yourself:

<?php
public function hookDefineAcl($args)
{
    $acl = $args['acl'];
    $acl->addResource('YourPlugin_YourRecords');
}

One last thing you may need to do is filter the select object in the record’s table class by overriding Omeka_Db_Table::getSelect(). This should protect unauthorized API users from viewing non-public records:

<?php
public function getSelect()
{
    $select = parent::getSelect();
    $permissions = new Omeka_Db_Select_PublicPermissions('YourPlugin_YourRecords');
    // Where "your_records" is the table alias, "owner_column" is the user column to check against,
    // and "public_column" is the permissions column to check against.
    $permissions->apply($select, 'your_records', 'owner_column', 'public_column');
    return $select;
}

Extending Existing Resources

You can extend the representations of existing resources by using the api_extend_<resource> filter, where <resource> is the resource you want to extend.

<?php
protected $_filters = array('api_extend_items');

public function filterApiExtendItems($extend, $args)
{
    $item = $args['record'];

    // For one resource:
    $resourceId = $this->_db->getTable('YourResource')->findByItemId($item->id);
    $extend['your_resources'] = array(
        'id' => 1,
        'url' => Omeka_Record_Api_AbstractRecordAdapter::getResourceUrl("/your_resources/{$resourceId->id}"),
        'resource' => 'your_resources',
    );

    // Or, for multiple resources:
    $extend['your_resources'] = array(
        'count' => 10,
        'url' => Omeka_Record_Api_AbstractRecordAdapter::getResourceUrl("/your_resources?item={$item->id}"),
        'resource' => 'your_resources',
    );

    return $extend;
}

Note that the API enforces a pattern when extending a resource:

  • id and url for a one-to-one relationship
  • count and url for a one-to-many relationship
  • resource is recommended but not required

All other keys pass through as custom data that may be used for the client’s convenience.