text: const mongoose = require('mongoose');
  
  const Schema = mongoose.Schema;
  
  const BookSchema = new Schema({
    title: { type: String, required: true },
    author: { type: Schema.Types.ObjectId, ref: 'Author', required: true },
    summary: { type: String, required: true },
    isbn: { type: String, required: true },
    genre: [{ type: Schema.Types.ObjectId, ref: 'Genre' }],
  });
  
  BookSchema.virtual('url').get(function () {
    return '/catalog/book/' + this._id;
  });
  
  module.exports = mongoose.model('Book', BookSchema);
  