javascript - DynamoDB - Update or Create if not found method -

in dynamodb, how can make update or create if not found method if have hash key , range key in table. below works if have table hash key, not tables hash , range key:

 var save = function(user_id, store_id, callback){      var doc = require('dynamodb-doc'),     docclient = new doc.dynamodb();      var params = {         tablename: 'stores',         returnvalues: 'none',         key: {             'user_id': user_id         },         conditionexpression: "#a = :store_id_val",         updateexpression: 'set #a = :store_id_val',         expressionattributenames: {             '#a': 'store_id'         },         expressionattributevalues: {             ':store_id_val': store_id         }     };      // save dynamodb document     docclient.updateitem(params, function(error, response) {         return callback(error, response);     });   } 

it simple. need specify both hash , range key in key parameter. can away this:

var save = function(user_id, store_id, callback) {      var doc = require('dynamodb-doc'),         docclient = new doc.dynamodb();      var params = {         tablename: 'stores',         returnvalues: 'none',         key: {             'user_id': user_id,             'store_id': store_id         }     };      // save dynamodb document     docclient.updateitem(params, function(error, response) {         return callback(error, response);     }); }