AngularJS and ngResouce, what's the magic?-Collection of common programming errors

I’m working currently on RESTful AngularJS $resource feature. I really don’t get all of the feature, even with examples provided by Angular Documentation or Stackoverflow similar subjects.

My usecase is simple :

1) I have a html list, fed with a json file. 2) I change the order via jQuery ui sortable 3) after changing, I would like the server to save the new position of each item of the list.

First and second steps are done : I can read a $resource that looks like this :

 function DndCtrl($scope, $resource) {
   var feed = $resource('/users/'+ userId +'/test.json');
   $scope.tests = feed.query();
 }

json file returns items with position and a description.

and display it via html classical Angular call :

When ordering via ui.sortable, I can manage to look at the change with $index+1

But here’s the last step : how to save the change on server after sorting items ?

I tried this basic thing :

function update(index) {
 var ch = feed.get({id: index});
 ch.position = index+1;
 ch.$save();
}
$scope.updateSortable = {
 update: function(e, ui) {
   update(ui.item.index());
 },
 placeholder: "xp-hightlight",
 axis: 'y'
};

Error I have with this is:

TypeError: Object # has no method 'push'

I probably miss a logical thing somewhere but as I’m not yet at ease with RESTful model, I don’t know exactly what I did wrong 🙂

UPDATE

I just wanted to add a detail about json urls : the read list is available with this route :

 /users/:userId/tests (GET)

But each item is available at this route :

 /users/:userId/tests/:id   (PUT, DELETE)

Of course, in the get method, if I try to catch the second syntax, it returns a 404 Not Found.

SECOND UPDATE :

I tried to modify the call method with this :

function DndCtrl :

 var feed = $resource('/users/'+ userId +'/tests/:id', {'update': {method:"PUT", isArray:true}});

and in update function :

 var t=$scope.test[index].id;
 var ch = feed.get({id:t});
 ch.position = index+1;
 ch.$update();

It returns :

 Uncaught TypeError: Object # has no method '$update' controller.js?body=1:11
 GET http://rooturl/users/1/tests/20?update=%5Bobject+Object%5D 404 (Not Found)