node.js - Mongoose, is it possible to assign parent id to sub document on save in one call? -

i wondering if it's possible(or needed) provide subdocument reference it's parents id in 1 call. here code i'm working with:

var mongoose = require('mongoose'); var schema = mongoose.schema;  var latlng = new schema({   id: schema.objectid,   created_at: date,   accuracy: {     type: number,     required: true   },   latitude: {     type: number,     required: true   },   longitude: {     type: number,     required: true   },   _walk: {     type: schema.objectid,     ref: 'walk',     required: true   } }); latlng.pre('save', function(next){   if(!this.created_at)     this.created_at = new date(); });  var walk = new schema({   id: schema.objectid,   created_at: date,   updated_at: date,   description: string,   elapsedtime: number,   distance: number,   waypoints: [latlng],   _user: {     type: schema.objectid,     ref: 'user',     required: true   } });  walk.pre('save', function(next){   var = new date();   this.updated_at = now;   if(!this.created_at)     this.created_at = now;   next(); });  walk.pre('update', function(next){   this.updated_at = new date(); });  walk.pre('findoneandupdate', function(next){   this.updated_at = new date(); });  walk.pre('findbyidandupdate', function(next){   this.updated_at = new date(); });  module.exports = mongoose.model('walk', walk); 

wondering if there's way, maybe in latlng.pre('save'), assign latlng._walk walk.id?

so when like:

var walk = new walk({     description: req.body.description,     elapsedtime: req.body.elapsedtime,     distance: req.body.distance,     waypoints: req.body.waypoints,     _user: req.user._id   }); 

it allow me call walk.save() , not have iterate through waypoints , manually assign _walk walk._id

i hope makes sense, help!

if need why not manually create before , save document it. can generate objectid instead of letting mongo handle it. there nothing against that.