node.js - Mongoose distinct with promises -

i use when.js promise library mongoose , try distinct filed of collection , return result promise

 mongoose.promise= require("when");   function getpromiseddistinct(startdate, enddate) {     return when.promise(function(resolve, reject) {         $log.distinct("keys", {                 datetime: {                     "$gte": startdate,                     "$lt": enddate                 }             }).exec()             .then(function(res) {                 return resolve(res);             });     });  } 

however getpromiseddistinct resolved promise function

function (resolve, reject) {     if (!_this.op) {       callback && callback(null, undefined);       resolve();       return;     }      _this[_this.op].call(_this, function(error, res) {       if (error) {         callback && callback(error);         reject(error);         return;       }       callback && callback.apply(null, arguments);       resolve(res);     });   } 

edit #1 getpromiseddistinct called as

    function agg(day, startdate, enddate) {       return when.promise(function(resolve, reject) {         getpromiseddistinct(startdate, enddate).then(function(keys) {             log.data("keys : \n" + licence_keys);         }).otherwise(function(keys) {             return reject(err);         });     }); } 

why not resolved value?

you've instructed mongoose use when.js promise library. if works native promises (and seemingly bluebird , q) don't need wrap queries in promise, mongoose (once use exec()) code written such:

function getpromiseddistinct(startdate, enddate) {     return $log.distinct("keys", {                 datetime: {                     "$gte": startdate,                     "$lt": enddate                 }             }).exec()     });  } 

you can same agg function.

as @robertklep pointed out in comments there no need include then block in getpromiseddistinct because it's unnecessary clutter (see promise anti-patterns. returning promise object return $log.distinct... , accessing value in agg function.

it's worth taking note of mongoose's documentation on plugging in promises library:

mongoose tests es6 native promises, bluebird, , q. promise library exports es6-style promise constructor should work in theory, theory differs practice. if find bug, open issue on github