toValue :: forall a.  PersistField a => Either a [a] -> DB.Value
toValue val =
    case val of
      Left v   -> DB.val $ toPersistValue v
      Right vs -> DB.val $ map toPersistValue vs
toValue :: forall a.  PersistField a => Either a [a] -> DB.Value
toValue val =
    case val of
      Left v   -> DB.val $ toPersistValue v
      Right vs -> DB.val $ map toPersistValue vs
toValue val =
    case val of
      Left v   -> DB.val $ toPersistValue v
      Right vs -> DB.val $ map toPersistValue vs