Recursively flatten nested Hashes

hash_extension.rb

class Hash
  def flatten_nested(hash = {}, prefix = '')
    each do |key, value|
      full_key = prefix.empty? ? key : "#{prefix}_#{key}"
      value.is_a?(Hash) ? value.flatten_nested(hash, full_key) : hash[full_key] = value
    end
    hash
  end
end