node.jsmongodbmongoosepopulate

Mongoose Populate returning null or undefined


I'm sorry if this is a n00b question, I've been searching Google & Stack for hours now and I've got to ask!

I have two schemas, User and Story, shown below. I am trying to reference the User for a Story using the Ref option to Populate in a Query - I've using mySQL before and so wanted to try to replicate a JOIN statement. Whenever I try to use populate I just get the objectID returned, or null (shown below).

Edited 12 Nov to fix hardcoded IDs & add console data

story-schema.js

var mongoose = require('mongoose'),
Schema = mongoose.Schema,
User = require('./user-schema');

var StorySchema = new Schema({  
title: { type: String, required: true },  
author_id: { type: Schema.Types.ObjectId, ref: 'User' },
summary: { type: String, required: true },
rating: { type: String, required: true }
});

module.exports = mongoose.model('Story', StorySchema, 'stories');

user-schema.js

var mongoose = require('mongoose'),
Schema = mongoose.Schema;

var UserSchema = new Schema({
    username: { type: String, required: true, index: { unique: true } },
    is_admin: {type: Boolean, required: true, default: false }
});

save - id hardcoded for example

app.post('/api/new_story', function(req, res){
var story;
story = new Story({
    title: req.body.title,
    author_id: mongoose.Types.ObjectId(req.params._id), 
            /* ex of req.params._id: 527fc8ff241cdb8c09000003*/
    summary: req.body.summary,
    rating: req.body.rating
});

story.save(function(err) {
    if (!err) {
        return console.log("created");
    } else {
        return console.log(err);
    }
});
return res.send(story);
});

example user when logged in terminal

{
"__v" : 0,
"_id" : ObjectId("527fc8ff241cdb8c09000003"),
"is_admin" : false,
"username" : "ted"
}

example story when logged in terminal

{
"title" : "Test Story",
"author_id" : "527fc8ff241cdb8c09000003",
"summary" : "Test summary",
"rating" : "12",
"_id" : ObjectId("52827692496c16070b000002"),
"__v" : 0
}

queries

//other mongoose/app includes above
User = require('./config/schema/user-model'),
Story = require('./config/schema/story-model');

// data.author_id = 527fc8ff241cdb8c09000003 
// data.author_id.username = undefined
app.get('/api/query/:id', function (req, res){
return Story.findOne({_id:req.params.id})
.populate( { path: 'User' } )
.exec(function (err, data) {
            console.log(data.author_id);
            console.log(data.author_id.username);
          if (err) {
            return res.json({error:err})
          }
        })
});

// data.author_id = null 
app.get('/api/query2/:id', function (req, res){
return Story.findOne({_id:req.params.id}) //_id hardcoded for example
.populate( 'author_id' )
.exec(function (err, data) {
            console.log(data.author_id);
          if (err) {
            return res.json({error:err})
          }
        })
});

In the first query I get the author_id I already saved back, which kind of makes sense as that's what I saved - but I access the username.

In the second query I can't even access the author_id I've already saved.

Edit: I can run a normal GET query fine without the 'populate'

What I'd like to happen

Is to be able to access the author information from the story - this is more like a proof of concept. Eventually I'd like to reference the Story _id in the the User model as there can be many Stories to a User, but only one User per Story but thought I'd start here first.


Solution

  • Since your example includes raw Object IDs not even quoted as valid javascript strings, it's hard to understand what is a mistake in your question vs a mistake in your code, but mostly your second query looks like it should work. I suspect you are mixing up your ObjectId values. You are using the same ObjectId for your story and your user and that won't work:

       author_id: mongoose.Types.ObjectId(528149b38da5b85003000002),
    

    That's the same ID you use to lookup the story. So I think the fix is:

    1. Make sure you have a valid user record in the users collection
    2. Make sure your test story record's story.author_id matches that
    3. Make sure you are looking up the story by the story Id and not the author_id.

    If you still can't get this working, code the entire thing in a single .js file with both schemas, both models, and some code to create the records then do the queries, and post that.