node.js - How to effectively fetch comments for posts with MongoDB/mongoose? -

i have following post , collection documents:

// posts {     "_id" : objectid("56978d8cdbc511a81e7e2ea8"),     "body" : "post body 1",     "created_at" : 1452772748737 }, {     "_id" : objectid("56978d3cdbc655b81e7e2e10"),     "body" : "post body 2",     "created_at" : 1452772759731 }  // comments {     "_post" : objectid("56978d8cdbc511a81e7e2ea8"),     "body" : "comment 1" }, {     "_post" : objectid("56978d3cdbc655b81e7e2e10"),     "body" : "comment 2" } 

i need query posts comments following result:

{     "_id" : objectid("56978d8cdbc511a81e7e2ea8"),     "body" : "post body 1",     "created_at" : 1452772748737,     "comments": [{         "_post" : objectid("56978d8cdbc511a81e7e2ea8"),         "body" : "comment 1"     }] }, {     "_id" : objectid("56978d3cdbc655b81e7e2e10"),     "body" : "post body 2",     "created_at" : 1452772759731,     "comments": [{         "_post" : objectid("56978d3cdbc655b81e7e2e10"),         "body" : "comment 2"     }] } 

my schema post , collections following:

// post  var postschema = mongoose.schema({  },{     strict: "throw",     collection: "posts" });  postschema.add({     created_at: {         type: number,         'default': date.now     } });  postschema.add({     title: {         type: string     } });  postschema.add({     body: {         type: string     } });  // comment var commentschema = mongoose.schema({  },{     strict: "throw",     collection: "comments" });  commentschema.add({     _post: {         type: mongoose.schema.types.objectid,         ref: 'post'     } });  commentschema.add({     body: {         type: string     } }); 

what way result above?

try through mongoose populate , aggregate. sample codes below.

var post = mongoose.model('post', postschema); var comment = mongoose.model('comment', commentschema);  comment.aggregate([     {$group: {_id: '$_post', comments: {$push: '$body'}}}     // ...     ], function(err, result) {         if (err)            // error handling         post.populate(result, {path: "_id"}, function(err, ret) {             if(err)                 console.log(err);             else                 console.log(ret);         }); });