mongodb - Mongoose Caching a Part of a Referenced Subdoc on Creation -

i have simple schema references. dont want populate referenced document on every query. instead want cache part (only single attribute) on referencing document.

a simple example schema:

user   - displayname   (....stuff....)  posts   - title   - content   - user (reference?) 

when used references , population on demand postschema like:

var postschema = new schema({     ...     user: {             type: schema.objectid,             ref: 'user'         } }) 

but want save (cache) only displayname (not other stuff in user) , _id in post when created. thougts on change postschema following:

user: {     _id: {         type: schema.objectid,         ref: 'user'     },     displayname: string } 

on creation of post do:

var post = new post(req.body); post.user._id = req.user._id; post.user.displayname = req.user.displayname; 

the problem is: looks _id is referenced user, leading absurd user._id._id. iscreator-middleware needs convert _id string:

exports.iscreator = function(req, res, next) {     if (req.post.user._id.tostring() !== req.user._id.tostring()) {         return res.status(403).send('user not authorized');     }     next(); }; 

this cannot best solution. question is: best practice case?