node.js：JSON 点表示法 + 访问数组键

Question

我有一个使用 node.js、express、mongoDB 和 mongoose 的站点设置。 Mongoose 给了我一个包含这个的数组：

[ { title: 'HTML in depth',
    author: 'kevin vanhove',
    _id: 53039f264a6324978c70084b,
    chapters: 
     [ { _id: 53039f264a6324978c70084d,
         content: '/jow',
         title: 'History of HTML' },
       { _id: 53039f264a6324978c70084c,
         content: '/w3c',
         title: 'What is the W3C' } ],
    __v: 0 } ]

我正在使用此代码在我的终端中获得此结果：

function indexData(books){

console.log(books)

res.render("index.html", {context:books, partials:{footer:"footer", header:"header"}})

}

现在我正在尝试访问 chapters[0].title 中的值，但出现错误：

console.log(books[0].chapters[0].title)

TypeError: Cannot read property '0' of undefined

我在这里感到困惑，我是否使用正确的点符号访问该值？

更新 1：完成终端输出

24 Feb 10:56:47 - [nodemon] restarting due to changes...
24 Feb 10:56:47 - [nodemon] starting `node app.js`
Mongoose: books.find({}) { fields: undefined }  

/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/routes/routes.js:45
        console.log(books[0].chapters[0].title)
                                     ^
TypeError: Cannot read property '0' of undefined
    at indexData (/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/routes/routes.js:45:32)
    at Promise.<anonymous> (/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/routes/routes.js:37:31)
    at Promise.<anonymous> (/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/node_modules/mongoose/node_modules/mpromise/lib/promise.js:177:8)
    at Promise.EventEmitter.emit (events.js:95:17)
    at Promise.emit (/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/node_modules/mongoose/node_modules/mpromise/lib/promise.js:84:38)
    at Promise.fulfill (/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/node_modules/mongoose/node_modules/mpromise/lib/promise.js:97:20)
    at /Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/node_modules/mongoose/lib/query.js:1052:26
    at model.Document.init (/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/node_modules/mongoose/lib/document.js:250:11)
    at completeMany (/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/node_modules/mongoose/lib/query.js:1050:12)
    at Object.cb (/Users/kevinvanhove/Documents/work/projects/basing/business/klanten/javascript/nodeJS/express/basing/node_modules/mongoose/lib/query.js:1017:11)
24 Feb 10:56:49 - [nodemon] app crashed - waiting for file changes before starting...

部分解决方案：

我试图获取章节数据。更新我的猫鼬模式以包含章节数据就可以了。

var booksSchema = new mongoose.Schema({
 title: String,
 author: String,
 chapters: [
    {
        title: String,
        content: String
    }
 ]

});

Answer 1

这在 Mongoose（服务器）端不起作用。 find() 的结果是一个 cursor，您需要从本机驱动程序部分通过 toArray 进行迭代或转换。像这样的

（假设架构Books）：

Books.collection.find({}).toArray(function(err, results) {

  // results is an array that you can do something with here.

});

当然，如果您为数组及其文档定义了 不是 embedded 的附加架构，那么这会带来更多伤害，您需要使用迭代方法来获取您的结果为数组。

如果您想要books 中的特定 项和其中的子项，那么您最好使用operators 调整您的查找查询，而不是返回所有结果。甚至aggregation pipeline 也可能会有所帮助。