As Fals mentionned in the comment, the articleId parameter was in the request content. So I made a little trick to have it also on the URI.
angular.module('ADI.Resources').factory("Articles", ['$resource', function($resource) {
return $resource('/api/v1/article/:articleId', {
articleId: '@_id',
_shop: window.user._shop
}, {
update: {
method: 'PUT',
params: {
articleId: "@articleId"
}
}
});
}]);