// This is a contrived example to demonstrate duplicating
// data on both sides of a relationship to enable population

var PostSchema = new mongoose.Schema({
  title: String,
  slug: String,
  contents: String,
  categories: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Category' }]
});

var Post = mongoose.model('Post', PostSchema);

var CategorySchema = new mongoose.Schema({
  name: String,
  posts: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Post' }]
});

var Category = mongoose.model('Category', CategorySchema);

// now we can populate on both sides

Post.find().populate('categories').exec(function(err, posts) { /* ... */ });
Category.find().populate('posts').exec(function(err, categories) { /* ... */ });