text: /**
   * This module defines a schema of school Classes.
   * It using mongoose as framework.
   *
   * @type {Schema}
   */
  
  const mongoose = require('mongoose');
  let Schema = mongoose.Schema;
  
  let schoolClass = new Schema({
      grade: {type: String, required: true},
      letter: {type: String, required: false},
      students: [{type: Schema.Types.ObjectId, ref: 'student', required: false}],
      studentSize: {type: Number, required: false}
  });
  
  module.exports = schoolClass;