Converting nested hash keys from CamelCase to snake_case in Ruby

If you use Rails:

Example with hash: camelCase to snake_case:

hash = { camelCase: 'value1', changeMe: 'value2' }

hash.transform_keys { |key| key.to_s.underscore }
# => { "camel_case" => "value1", "change_me" => "value2" }

source:
http://apidock.com/rails/v4.0.2/Hash/transform_keys

For nested attributes use deep_transform_keys instead of transform_keys, example:

hash = { camelCase: 'value1', changeMe: { hereToo: { andMe: 'thanks' } } }

hash.deep_transform_keys { |key| key.to_s.underscore }
# => {"camel_case"=>"value1", "change_me"=>{"here_too"=>{"and_me"=>"thanks"}}}

source: http://apidock.com/rails/v4.2.7/Hash/deep_transform_keys