gistfile1.rb

params = {
  "root_elements_without_brackets"=>[
    {"key"=>"value1"}, 
    {"key"=>"value2"}, 
  ],
  "root_elements[]"=>[
    {"key"=>"value1"}, 
    {"key"=>"value2"}, 
  ],
  "resource" => {
    "child_elements[]"=>[
      {"key"=>"value1"}, 
      {"key"=>"value2"}, 
    ],
    "child_elements_without_brackets"=>[
      {"key"=>"value1"}, 
      {"key"=>"value2"}, 
    ]
  }
}

uri = URI.parse('http://store.dev/')
client = RestClient::Resource.new(uri.to_s)
client.post(params, {:accept => :html})

# Started POST "/" for 127.0.0.1 at 2013-12-27 11:42:15 +0400
#   Parameters: {
#     "root_elements_without_brackets"=>{"key"=>"value2"}, 
#     "root_elements"=>[{"key"=>"value1"}, {"key"=>"value2"}], 
#     "resource"=>{
#       "child_elements"=>[{"key"=>"value2"}], 
#       "child_elements_without_brackets"=>{"key"=>"value2"}
#     }
#   }