node.js 要求返回一个空对象
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Require returns an empty object
提问by user3677173
I have a folder, that has index.js and a couple of models (classes) index.js
我有一个文件夹，里面有 index.js 和几个模型（类）index.js
module.exports = {
Book : require('./book'),
Author : require('./author')
}
book.js
书.js
var Author = require('./author')
var Book = models.ActiveRecord.extend({
schema : {
belongsTo : {
author : Author
}
}
})
module.exports = Book
author.js
作者.js
var Book = require('./book')
var Author = models.ActiveRecord.extend({
schema : {
hasMany : {
author : Book
}
}
})
module.exports = Author
The problem is that Author class does not seem to find the Book! It's just an empty Object. However, if I switch the exports in index.js, putting Book after Author - it works, but then the other model stops working.
问题是 Author 类似乎没有找到 Book！它只是一个空对象。但是，如果我在 index.js 中切换导出，将 Book 放在 Author 之后 - 它可以工作，但另一个模型会停止工作。
I don't want to do any hacks to make it work.
我不想做任何黑客来让它工作。
回答by B T
This is because you have a circular dependency. Node.js handles this in a very specific way:
这是因为您有循环依赖。Node.js 以一种非常具体的方式处理这个问题：
The first module loads and runs (in this case,
book.js). It (book.js) will load and run the second module (author.js) when it (book.js) requires the other (author.js)When the second module (
author.js) is loaded and run, it (author.js) requires the first module (book.js) but it (author.js) will receive a partially filledobject - however many things were set on the exports in book.js before it required author.js will be in that objectAfter
book.jsis completely run through, the objectauthor.jsgot fromrequire('./book')will be the fullbook.jsmodule object
第一个模块加载并运行（在本例中为
book.js）。它 (book.js) 将加载并运行第二个模块 (author.js) 当它 (book.js) 需要另一个 (author.js)当第二个模块 (
author.js) 加载并运行时，它 (author.js) 需要第一个模块 (book.js) 但它 (author.js) 将收到一个部分填充的对象 - 但是在 book.js 中的导出上设置了很多东西，然后才需要 author.js在那个对象中book.js完全运行后，author.js从中得到的对象require('./book')将是完整的book.js模块对象
For more info, here's the docs: http://nodejs.org/api/modules.html
有关更多信息，请参阅文档：http: //nodejs.org/api/modules.html
If its possible to dynamically add that schema to one of those ActiveRecord objects, that's one way to solve this. This is actually kind of a tricky situation. In fact, even without the module system, this would cause problems for you. If you put all this code in one file, how would you make it work?
如果可以将该模式动态添加到这些 ActiveRecord 对象之一，这是解决此问题的一种方法。这实际上是一种棘手的情况。事实上，即使没有模块系统，这也会给你带来问题。如果你把所有这些代码放在一个文件中，你会如何让它工作？
