text: /**
   * This module defines a schema of lectures.
   * It using mongoose as framework.
   *
   * @type {Schema}
   */
  
  const mongoose = require('mongoose');
  let Schema = mongoose.Schema;
  
  let lecture = new Schema({
    teacher: {type: Schema.Types.ObjectId, ref:'teacher', required: false},
    room: {type: Schema.Types.ObjectId, ref:'room', required: false},
    course: {type: Schema.Types.ObjectId, ref:'course', required: false},
    subject: {type: Schema.Types.ObjectId, ref:'subject', required: false},
    period: {type: Schema.Types.ObjectId, ref:'period', required: false},
    pinned: {type: Boolean, required: false},
  });
  
  module.exports = lecture;