Populate nested array in mongoose

Mongoose 4.5 support this

Project.find(query)
  .populate({ 
     path: 'pages',
     populate: {
       path: 'components',
       model: 'Component'
     } 
  })
  .exec(function(err, docs) {});

And you can join more than one deep level.

Edit 03/17/2021: This is the library's implementation, what it do behind the scene is make another query to fetch thing for you and then join in memory. Although this work but we really should not rely on. It will make your db design look like SQL tables. This is costly operation and does not scale well. Please try to design your document so that it reduce join.

That works for me:

 Project.find(query)
  .lean()
  .populate({ path: 'pages' })
  .exec(function(err, docs) {

    var options = {
      path: 'pages.components',
      model: 'Component'
    };

    if (err) return res.json(500);
    Project.populate(docs, options, function (err, projects) {
      res.json(projects);
    });
  });

Documentation: Model.populate

As others have noted, Mongoose 4 supports this. It is very important to note that you can recurse deeper than one level too, if needed—though it is not noted in the docs:

Project.findOne({name: req.query.name})
    .populate({
        path: 'threads',
        populate: {
            path: 'messages', 
            model: 'Message',
            populate: {
                path: 'user',
                model: 'User'
            }
        }
    })

You can populate multiple nested documents like this.

   Project.find(query)
    .populate({ 
      path: 'pages',
      populate: [{
       path: 'components',
       model: 'Component'
      },{
        path: 'AnotherRef',
        model: 'AnotherRef',
        select: 'firstname lastname'
      }] 
   })
   .exec(function(err, docs) {});