Refactoring

gistfile1.rb

class Foo
  include Mongoid::Document

  field :bar, :type => Array
end

# ruby-1.9.2-p0 > Foo.create(:bars => [1,2,3])
#  => #<Foo _id: 4d1128c4fddc0d2146000001, bars: [1, 2, 3]>
# ruby-1.9.2-p0 > Foo.first.bars
#  => [1, 2, 3]

# After some refactoring...
class Foo
  include Mongoid::Document

  embeds_many :bars
end

class Bar
  include Mongoid::Document

  field :value, :type => Integer

  embedded_in :foo, :inverse_of => :bars
end

# ruby-1.9.2-p0 > Foo.first.bars
# NoMethodError: undefined method `klass' for 1:Fixnum
# 	from mongoid-2.0.0.beta.20/lib/mongoid/associations/embeds_many.rb:232:in `block in build_children_from_attributes'
# 	from mongoid-2.0.0.beta.20/lib/mongoid/associations/embeds_many.rb:231:in `each'
# 	from mongoid-2.0.0.beta.20/lib/mongoid/associations/embeds_many.rb:231:in `each_with_index'
# 	from mongoid-2.0.0.beta.20/lib/mongoid/associations/embeds_many.rb:231:in `build_children_from_attributes'
# 	from mongoid-2.0.0.beta.20/lib/mongoid/associations/embeds_many.rb:147:in `initialize'
# 	from mongoid-2.0.0.beta.20/lib/mongoid/associations.rb:285:in `new'
# 	from mongoid-2.0.0.beta.20/lib/mongoid/associations.rb:285:in `block (2 levels) in associate'
# 	from mongoid-2.0.0.beta.20/lib/mongoid/memoization.rb:11:in `memoized'
# 	from mongoid-2.0.0.beta.20/lib/mongoid/associations.rb:284:in `block in associate'
# ...

# You can use attributes to migrate existing data.
#
# ruby-1.9.2-p0 > f = Foo.first
#  => #<Foo _id: 4d1128c4fddc0d2146000001, > 
# ruby-1.9.2-p0 > f.attributes['bars']
#  => [1, 2, 3] 
# ruby-1.9.2-p0 > f.bars = f.attributes['bars'].map {|bar| Bar.new(:value => bar)}
#  => [#<Bar _id: 4d113271fddc0d222a000005, value: 1>, #<Bar _id: 4d113271fddc0d222a000006, value: 2>, #<Bar _id: 4d113271fddc0d222a000007, value: 3>] 
# ruby-1.9.2-p0 > f.save
#  => true 
# ruby-1.9.2-p0 > f.bars
#  => [#<Bar _id: 4d113271fddc0d222a000005, value: 1>, #<Bar _id: 4d113271fddc0d222a000006, value: 2>, #<Bar _id: 4d113271fddc0d222a000007, value: 3>]