async function findOne (dbName, id) {
  const res = await dbAction(dbName, 'findOne', {
    _id: id
  })
  if (!res) {
    return res
  }
  const { _id, ...rest } = res
  return {
    id: _id,
    ...decObj(rest)
  }
}
get doc from db
@param {string} dbName
@param {string} id
@return any