We have this code:

class Band
include Mongoid::Document
has_many :albums
end

class Album
include Mongoid::Document
belongs_to :band
end

@bands = Band.includes(:albums).entries

This is great because now I can run @bands.first.albums without hitting the DB.
But now, if we write this includes to the rails cache...

Rails.cache.write('bands', @bands)

...we then read the cache.

bands = Rails.cache.read('bands')

This returns an array of band documents...

#<Band _id: 536a53c969702d208f240000, created_at: 2014-05-07 15:39:53 UTC, updated_at: 2014-05-08 15:55:29 UTC, name: "Pink Floyd", fan_count: 394857, #<Band _id: 536adf2a69702d1574130000, created_at: 2014-05-08 01:34:34 UTC, updated_at: 2014-05-08 01:35:40 UTC, name: "Tool", fan_count: 2958394, #<Band _id: 536bcad169702d743e1e0000, created_at: 2014-05-08 18:20:01 UTC, updated_at: 2014-05-08 18:27:10 UTC, name: "My Morning Jacket", fan_count: 3945734

...and then we can't get the albums.

bands.first.albums

NoMethodError: undefined method 'albums' for #<Array:0x00000104df50c0>

Is there a special way to cache these eager loaded documents with Rails or Mongoid?

FYI we're using Mongoid 4.