Meteor Populate / Join (Quick & Dirty)

populate.js

// quick and dirty populating ("joining") in Meteor
Mongo.Collection.prototype.findAndPopulate = function (selector, options, populates) {
  /*
    selector and options: from Mongo.Collection.prototype.find(selector, options)
    populates: [Object] or Object
               [{id, as, from}] or {id, as, from}
      e.g. {id: 'userId', as: 'thisUser', from: Users}
           will look up doc.userId in Users and assign to doc.thisUser
           --> doc.thisUser = Users.findOne(doc.userId);
  */
  check(populates, Match.OneOf(Object, Array));
  if (!_.isArray(populates)) {
    populates = [populates]; // always operate on an Array of Objects
  }
  const documents = this.find(selector, options).fetch();

  // build cache. only run one query for each collection populated from
  populates = populates.map(populate => {
    const ids = _.pluck(documents, populate.id);
    const query = {_id: {$in: ids}};
    populate.cache = _.indexBy(
      populate.from.find(query).fetch(),
      '_id' // index by id so it's fast to find for each document
    );
    return populate;
  });

  // populate each document individually
  return documents.map(doc => {
    // run each populate
    populates.forEach(populate => {
      // fetch from cache
      doc[populate.as] = populate.cache[doc[populate.id]];
    });
    return doc;
  });
};