old_contents: 'use strict';
  
  /*!
   * Module dependencies.
   */
  
  const mongoose = require('mongoose'),
        async    = require('async'),
        Link     = mongoose.model('Link');
  
  /*!
   * Expos
   */
  
  exports.index = (req, res, next) => {};
  
new_contents: 'use strict';
  
  /*!
   * Module dependencies.
   */
  
  const mongoose = require('mongoose'),
        async    = require('async');
  
  /*!
   * Expos
   */
  
  exports.index = (req, res, next) => {};
  
subject: add remove Link model