I would like to know how to pass headers to AngularJS $resource method

Here is the factory method

.factory('DataRepository', function ($resource) {

return $resource(serviceUrlPrefix + '/api/v1/AppList/:id', { id: '@id' }, { 'query': { method: 'GET', isArray: false }, 'update': { method: 'PUT', AppList: '@req', headers: { 'X-Requested-With': 'XmlHttpRequest' } } });

});

Here is the call to the dataRepository

dataRepository.update({ id: req[uniqueIDColumn] }, req, function (data) {

},

function (error) {

});

This code works fine. But i have few queries

Question 1:

Rather than specifying the headers in the factory method , how can i specify it in the call to the factory method? I tried few methods but it didnt work out.

Question 2:

I specified the header in the update method in the factory. When i perform "Save" using that factory, that header has been taken by default. But i have specified it explicitly for PUT method. Right? Why and how?

Question 3:

If i would like to specify the header for the particular factory in common for all Http methods, what is the way to do it?

Question 4:

What is the nomenclature for passing the parameters and the significance of "@" symbol before parameter and also in the below part, AppList is the parameter name used in the WebAPI, is it mandatory that it should match the parameter name in the WebAPI method, if its not matching, its not working:(

AppList: '@req'