猫鼬模型是另一个模型的后挂钩内的空对象

问题描述

我的项目有2个相互参照的模型.当删除一个模型的实例时，remove()方法将钩住另一个模型以删除依赖关系.

photo.model.js

const Album = require('./album');
       .
       .
// post hook of photo.remove()
schema.post('remove', (photo, next) => {

  console.log(Album);  // return empty obj {}

  Album.findById(photo._album, (error, album) => {
        // find album and remove photo
    });
});

删除里面的相册模型钩子返回空对象.我通过在钩子内部移动require语句找到了解决方法.

schema.post('remove', (photo, next) => {
  const Album = require('./album');
  Album.findById(photo._album, (error, album) => {
        // find album and remove photo
    });
});

但是该修复程序对我来说很难看，我的猜测是每次调用photo.remove()时都会调用require语句.

---

问题:

• 我上面关于每次调用photo.remove()都会被调用require"的猜测是否正确?
• 为什么不能将require放置在钩子外部并且与内部行为相同?
• 无论如何，我可以将require放置在钩子外部并获得与放置在钩子中相同的行为吗?

解决方案

听起来像您有周期性依赖关系，其中photo.model.js需要album.js，而photo.model.js需要... c

要解决此问题，可以使用以下方法:

const mongoose = require('mongoose');

schema.post('remove', (photo, next) => {
  mongoose.model('Album').findById(photo._album, (error, album) => {
    // find album and remove photo
  });
});

My project has 2 models referring to one another. When the instances of one model are removed, remove() method will hook another model to remove the dependencies.

photo.model.js

const Album = require('./album');
       .
       .
// post hook of photo.remove()
schema.post('remove', (photo, next) => {

  console.log(Album);  // return empty obj {}

  Album.findById(photo._album, (error, album) => {
        // find album and remove photo
    });
});

Album model inside remove hook return empty object. I found the fix by moving require statement inside the hook.

schema.post('remove', (photo, next) => {
  const Album = require('./album');
  Album.findById(photo._album, (error, album) => {
        // find album and remove photo
    });
});

But the fix looks ugly to me and my guess is every time photo.remove() is called require statement is called.

---

Question:

• Is my guess above about "require getting called every time photo.remove() is called" correct?
• Why can't I place the require outside the hook and having same behavior as inside?
• Is there anyway I can place require outside the hook and get the same behavior as placing it inside?

解决方案

It sounds like you have a cyclic dependency, where photo.model.js requires album.js which requires photo.model.js, ...

To work around that, you can use this:

const mongoose = require('mongoose');

schema.post('remove', (photo, next) => {
  mongoose.model('Album').findById(photo._album, (error, album) => {
    // find album and remove photo
  });
});

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