Specifying available HTTP methods for each field

Your resource may need a public field that isn't actually a property or field. RESTful provides a solution for this, and in 2.x it's very flexible.

In RESTful 1.x, you could specify create_or_update_passthrough in your public field definitions.

"create_or_update_passthrough": Determines if a public field that isn't mapped to any property or field, may be passed upon create or update of an entity. Defaults to FALSE.

In RESTful 2.x, instead of create_or_update_passthrough you may specify the HTTP methods that should be available for each field. An example should clarify the concept:

$public_fields['barry'] = array(
  // your field definition here...
  'methods' => array(RequestInterface::METHOD_GET, RequestInterface::METHOD_OPTIONS),
);

RequestInterface::METHOD_GET is a constant defined in RequestInterface; you could instead simply use the string GET. If you use the constant (and it's best practice to do so) then you will need to be sure to include the RequestInterface use statement:

use Drupal\restful\Http\RequestInterface;

If you examine that PHP interface, you will find the following METHOD constants:

  const METHOD_HEAD = 'HEAD';
  const METHOD_GET = 'GET';
  const METHOD_POST = 'POST';
  const METHOD_PUT = 'PUT';
  const METHOD_PATCH = 'PATCH';
  const METHOD_DELETE = 'DELETE';
  const METHOD_PURGE = 'PURGE';
  const METHOD_OPTIONS = 'OPTIONS';
  const METHOD_TRACE = 'TRACE';
  const METHOD_CONNECT = 'CONNECT';