ruby
class Dish
  include Mongoid::Document
end

class Dinner
  include Mongoid::Document
  embeds_many :dishes
end

>  Dinner.all.pluck(:id)
=> []

> Dinner.new.dishes.pluck(:id)
NoMethodError: undefined method `pluck' for #<Mongoid::Contextual::Memory:0x007f80618b9c58>
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/bundler/gems/mongoid-f9e6fdb1a67c/lib/mongoid/contextual.rb:20:in `pluck'
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/bundler/gems/mongoid-f9e6fdb1a67c/lib/mongoid/relations/embedded/many.rb:406:in `public_send'
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/bundler/gems/mongoid-f9e6fdb1a67c/lib/mongoid/relations/embedded/many.rb:406:in `block in method_missing'
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/bundler/gems/mongoid-f9e6fdb1a67c/lib/mongoid/scopable.rb:239:in `with_scope'
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/bundler/gems/mongoid-f9e6fdb1a67c/lib/mongoid/relations/embedded/many.rb:405:in `method_missing'
  from (irb):11
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.1.1/lib/rails/commands/console.rb:90:in `start'
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.1.1/lib/rails/commands/console.rb:9:in `start'
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.1.1/lib/rails/commands/commands_tasks.rb:69:in `console'
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.1.1/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
  from /Users/dblock/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.1.1/lib/rails/commands.rb:17:in `<top (required)>'
  from script/rails:5:in `require'
  from script/rails:5:in `<main>'