rest\Action $findModel

A PHP callable that will be called to return the model corresponding to the specified primary key value. If not set, findModel() will be used instead. The signature of the callable should be:

function ($id, $action) {
    // $id is the primary key value. If composite primary key, the key values
    // will be separated by comma.
    // $action is the action object currently running
}

The callable should return the model found, or throw an exception if not found.