old_contents: 'use strict';
  
  var mongoose = require('mongoose'),
      Schema = mongoose.Schema;
  
  var CourseSchema = new Schema({
    code: { type: String, required: true, unique: true, uppercase: true },
    title: { type: String, required: true },
    category: [ String ],
    subcategory: [String],
    prerequisite: [ { type: Schema.Types.ObjectId, ref: 'Course' } ],
  });
  
  // Virtuals 
  CourseSchema
    .virtual('canDoubleCount')
    .get(function(){
      return this.category.length > 1;
    });
  
  module.exports = mongoose.model('Course', CourseSchema);
new_contents: 'use strict';
  
  var mongoose = require('mongoose'),
      Schema = mongoose.Schema;
  
  var CourseSchema = new Schema({
    code: { type: String, required: true, unique: true, uppercase: true },
    title: { type: String, required: true },
    category: [ String ],
    subcategory: [String],
    prerequisite: [ { type: Schema.Types.ObjectId, ref: 'Course' } ],
    doubleCount: [{
      replace: String,
      freeUp: String
    }]
  });
  
  // Virtuals 
  CourseSchema
    .virtual('canDoubleCount')
    .get(function(){
      return this.category.length > 1;
    });
  
  module.exports = mongoose.model('Course', CourseSchema);
subject: Update the course model