javascript - 在 pug 布局文件中返回 undefined reference 对象和虚拟 getter，但从数据库中成功查询

Question

我的问题有两个方面，但我认为它们都是由同一个问题引起的:我的架构定义和/或模型创建。

我正在关注 this MDN Nodejs tutorial我想不通:

1. 为什么我的引用对象在我的布局文件中返回未定义，但我已经确认数据被正确插入和查询(据我所知)。

2. 我的虚拟 id getter 不工作。

架构定义:

book.js 斜体

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'}]

});

//this doesnt seem to be working. returns undefined on the
//object in layout file
BookSchema
.virtual('url')
.get(() => {
  return '/catalog/book/' + this._id;
});

module.exports = mongoose.model('Book', BookSchema);

author.js 斜体

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const AuthorSchema = new Schema({

  first_name: {type: String, required: true, max: 100},
  family_name: {type: String, required: true, max: 100},
  date_of_birth: {type: Date},
  date_of_death: {type: Date}

});

//Virtuals

AuthorSchema.virtual('name')
.get(() => {
  return this.family_name + ', ' + this.first_name;
});

//create virtual absolute url to obtain instance of this model
AuthorSchema.virtual('url')
.get(() => {
  return '/catalog/author/' + this._id;
});

module.exports = mongoose.model('Author', AuthorSchema);

模型创建:

function authorCreate(first_name, family_name, d_birth, d_death, cb) {
  authordetail = {first_name:first_name , family_name: family_name }
  if (d_birth != false) authordetail.date_of_birth = d_birth
  if (d_death != false) authordetail.date_of_death = d_death

  var author = new Author(authordetail);

  author.save(function (err) {
    if (err) {
      cb(err, null)
      return
    }
    console.log('New Author: ' + author);
    authors.push(author._id)
    cb(null, author)
  }  );
}

function bookCreate(title, summary, isbn, author, genre, cb) {
  bookdetail = {
    title: title,
    summary: summary,
    author: author,
    isbn: isbn
  }
  if (genre != false) bookdetail.genre = genre

  var book = new Book(bookdetail);
  book.save(function (err) {
    if (err) {
      cb(err, null)
      return
    }
    console.log('New Book: ' + book);
    books.push(book._id)
    cb(null, book)
  }  );
}

controller.js:

// Display list of all books.
exports.book_list = function(req, res) {

  Book.find({})
  .populate('author')//this seems to work
  .exec(function (err, list_books) {
    if (err) { return next(err); }
    //Successful, so render
    for(var b in list_books){
      console.log('author id: ' + list_books[b].author._id);//as evidenced here

    }

    //but the author object is undefined when rendered
    res.render('book_list', { title: 'Book List', book_list: list_books });

  });

};

layout.pug:

extends layout

block content
  h1= title
//url and author undefined here
  ul
    each book in book_list
      li
        a(href=book.url) #{book.title}
        |  #{book.author.name}

    else
      li There are no books.

截图:

工具:

• Node + Express js

• 哈巴狗

• mLab 免费套餐

我对 Mongoose DB 和 Pug 完全陌生，只知道教程中的入门书所教授的内容，并明确指出作为进一步阅读的内容。

如果您需要更多信息，请告诉我。谢谢

Answer 1

我的问题似乎是粗箭头函数的使用。将这些更改为常规 function() 语法解决了这个问题。

This answer确认它是 nodejs 中的支持问题。