javascript - Decrement many values simultaneously and positionally in mongodb -

i have collection representing robots holding inventory of products in positional slots, incremented , decremented.

{   _id: "someid",   name: "",   inventory: [{     productid: "productid1",     count: 30   }, {     productid: "productid2",     count: 56   }, {     // ... 55 slots.   }] } 

i have api interact document on put request. request data contain index of inventory update , number decrement by, eg:

[   { "inventory": 3, "inc": -10 },  // remove 10 robot.inventory[3]   { "inventory": 54, "inc": -2 },  // remove 2 robot.inventory[10] ] 

i have following code.

// robots submit api keep products date machineapiv1.addroute('/products', {   authrequired: true,   rolerequired: 'machine' }, {   put: function () {     // omit process data above     var user = users.findone(this.request.headers['x-user-id']);     robots.update(user.profiles.robot, {       $inc: { } // lost.     });   } }); 

i can't quite think of way in single update. how can increment multiple arbitrary indexes in mongo document?

mongodb makes simple - specify position in array of sub-documents want update:

robots.update(user.profiles.robot, {   $inc: {     'inventory.3.count': -10,     'inventory.54.count': -2   } });