I *believe* that we actually need to change the output slightly so that `$result` is an associative array - for example:

``` php
$positions = array();
// ...

$positions[] = array($position->getId()...);

return new JsonResponse(array('positions' => $positions));
```

(due to the warning from here: http://symfony.com/doc/current/components/http_foundation/introduction.html#creating-a-json-response)