javascript - How should I properly use populate with mongoose? -


i learning node , have been trying use mongoose. currently, goal learn how use populate.

i have projects definition , milestone require:

projectschema = new mongoose.schema({     id: string,     title: string,     description: string,     owner: string,     site: string,     creation_date: date,     milestone_ids: array,     milestones: [{         type: mongoose.schema.types.objectid,         ref: "milestone"     }] })  project = mongoose.model("project", projectschema) milestones = require(__dirname + "/milestones.js")();

then @ point in projects.js:

project.find(query, {}, {sort: {_id: -1}},     function (error, results) {         callback(results);     } ).populate("milestones");

how populate milestones?

here project data mongo:

{     "title": "sitename",     "description": "online thing",     "creation_date": {         "$date": "2013-07-11t19:45:42.139z"     },     "_id": {         "$oid": "51df0b66dbdd7c4f14000001"     },     "milestones": [],     "milestone_ids": [],     "__v": 0 }

and 1 milestone connected project:

{     "title": "proof of concept",     "description": "make work.",     "due_date": {         "$date": "2013-07-11t19:46:38.535z"     },     "project_id": "51df0b66dbdd7c4f14000001",     "_id": {         "$oid": "51df0b9edbdd7c4f14000002"     },     "__v": 0 }

also, milestone schema: 

milestoneschema = new mongoose.schema({     id: string,     title: string,     description: string,     owner: string,     site: string,     due_date: date,     project_id: {         type: string,         ref: "project"     } })  milestone = mongoose.model("milestone", milestoneschema);

you need order right of defining query options executing, , chainable apis such mongoose query can't know additional methods might call after query fires. when pass callback .find, mongoose sends query right away.

pass callback find

  • query defined arguments find
  • since callback there, query executes , issues command db
  • then .populate happens, has no effect query has been sent mongo

here's need do:

project.find(query, {}, {     sort: {         _id: -1     } }).populate("milestones").exec(function (error, results) {     callback(results); });

or little more readable:

project     .find(query)     .sort('-_id')     .populate('milestones')     .exec(function(error, results) {                           callback(results);     });

omit callback , use .exec

  • query passed .find creates query object parameters
  • additional chained calls .sort, .populate etc further configure query
  • .exec tells mongoose done configuring query , mongoose issues db command

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