Sails.js populate nested associations

Or you can use the built-in Blue Bird Promise feature to make it. (Working on [email protected])

See the codes below:

var _ = require('lodash');

...

Post
  .findOne(req.param('id'))
  .populate('user')
  .populate('comments')
  .then(function(post) {
    var commentUsers = User.find({
        id: _.pluck(post.comments, 'user')
          //_.pluck: Retrieves the value of a 'user' property from all elements in the post.comments collection.
      })
      .then(function(commentUsers) {
        return commentUsers;
      });
    return [post, commentUsers];
  })
  .spread(function(post, commentUsers) {
    commentUsers = _.indexBy(commentUsers, 'id');
    //_.indexBy: Creates an object composed of keys generated from the results of running each element of the collection through the given callback. The corresponding value of each key is the last element responsible for generating the key
    post.comments = _.map(post.comments, function(comment) {
      comment.user = commentUsers[comment.user];
      return comment;
    });
    res.json(post);
  })
  .catch(function(err) {
    return res.serverError(err);
  });

Some explanation:

1. I’m using the Lo-Dash to deal with the arrays. For more details, please refer to the Official Doc
2. Notice the return values inside the first “then” function, those objects “[post, commentUsers]” inside the array are also “promise” objects. Which means that they didn’t contain the value data when they first been executed, until they got the value. So that “spread” function will wait the acture value come and continue doing the rest stuffs.