DynamoDB: Support for nested records

[angerman]

I just came across the need for something like this:

getItem :: FromDynItem a => Text -> Item -> Parser a
getItem k m =
  case M.lookup k m of
    Nothing -> fail ("Key " <> T.unpack k <> " not found")
    Just (DMap dv) -> either (fail "...") return $ fromItem dv
    _       -> fail ("Key " <> T.unpack k <> " is not a map!")

which basically allows to use getItem like getAttr to produce nested
data types.