text: /**
   * option
   */
  
  'use strict'
  
  const db = require('./db').db
  
  //create self increament id
  exports.createDigitId = function* () {
  
  	let obj = yield db.collection('meta').findOneAndUpdate({
  		_id: '_digitId'
  	}, {
  		$inc: {
  			value: 1
  		}
  	}, {
  		returnOriginal: false
  	})
  
  	return Promise.resolve(obj.value.value)
  }