text: (function() {
      'use strict';
  
      var mongoose = require('mongoose'),
          Schema = mongoose.Schema;
  
      var QuestionSetSchema = new Schema({
          _id: Number,
          name: {
              type: String,
              validate: {
                  validator: function(v) {
                      return v.length<=200;
                  },
                  message: '{VALUE} is is too long!'
              }
          },
          description: String,
          user: String,
          createDate: Date,
          practiceTimes: Number,
          impact: Number,
          questions: [{
              type: Number,
              ref: 'Question'
          }],
          isDefault: Boolean,
          userPractice:[{
              practiceTimes:Number,
              user:String
          }]
      }, {
          collection: 'questionSets'
      });
      QuestionSetSchema.index({name: 1, user: 1}, {unique: true});
      module.exports = mongoose.model('QuestionSet', QuestionSetSchema);
  })();