Mongoose: deep population (populate a populated field)

I have Category model:

Category:
    ...
    articles: [{type:ObjectId, ref:'Article'}]

Article model contains ref to Account model.

Article:
    ...
    account: {type:ObjectId, ref:'Account'}

So, with populated articles Category model will be:

{ //category
    articles: //this field is populated
     [ { account: 52386c14fbb3e9ef28000001, // I want this field to be populated
         date: Fri Sep 20 2013 00:00:00 GMT+0400 (MSK),
         title: 'Article 1' } ],
    title: 'Category 1' }

The questions is: how to populate subfield (account) of a populated field ([articles])? Here is how I do it now:

globals.models.Category
    .find
        issue : req.params.id
        null
        sort:
            order: 1
    .populate("articles") # this populates only article field, article.account is not populated
    .exec (err, categories) ->
        console.log categories

I know it was discussed here: Mongoose: Populate a populated field but no real solution was found

Solution 1:

Firstly, update mongoose 3 to 4 & then use the simplest way for deep population in mongoose as below :

Suppose you have Blog schema having userId as ref Id & then in User you have some review as ref Id for schema Review. So Basically, you have three schema : 1. Blog 2. User 3. Review

And, you have to query from blog, which user owns this blog & the user review. So you can query your result as :

BlogModel
  .find({})
  .populate({
    path : 'userId',
    populate : {
      path : 'reviewId'
    }
  })
  .exec(function (err, res) {

  })

Solution 2:

Populating across multiple levels

Say you have a user schema which keeps track of the user's friends.

var userSchema = new Schema({
  name: String,
  friends: [{ type: ObjectId, ref: 'User' }]
});

Populate lets you get a list of a user's friends, but what if you also wanted a user's friends of friends? Specify the populate option to tell mongoose to populate the friends array of all the user's friends:

User.findOne({ name: 'Val' }).populate({
    path: 'friends',
    // Get friends of friends - populate the 'friends' array for every friend
    populate: { path: 'friends' }
});

Reference: http://mongoosejs.com/docs/populate.html#deep-populate

Solution 3:

Mongoose has now a new method Model.populate for deep associations:

https://github.com/Automattic/mongoose/issues/1377#issuecomment-15911192

Solution 4:

It might be a bit too late, but I wrote a Mongoose plugin to perform deep population at any arbitrary nested levels. With this plugin registered, you can populate category's articles and accounts with just a single line:

Category.deepPopulate(categories, 'articles.account', cb)

You can also specify populate options to control things like limit, select... for each populated path. Checkout the plugin documentation for more information.