function insert (dbName, inst) {
  let arr = isArray(inst) ? inst : [inst]
  arr = arr.map(obj => {
    const { id, _id, ...rest } = obj
    return {
      _id: _id || id || generate(),
      ...encObj(rest)
    }
  })
  return dbAction(dbName, 'insert', safeParse(arr))
}
db insert
@param {string} dbName
@param {object or array} inst