問題描述

我使用 Mongoose.js，無法解決 3 級層次文檔的問題.

I use Mongoose.js and cannot solve problem with 3 level hierarchy document.

有兩種方法.

第一 - 沒有參考.

C = new Schema({
    'title': String,
});

B = new Schema({
    'title': String,
    'c': [C]
});

A = new Schema({
    'title': String,
    'b': [B]
});

我需要顯示 C 記錄.我如何填充/找到它，只知道 C 的 _id?

I need to show C record. How can i populate / find it, knowing only _id of C?

我正在嘗試使用:

A.findOne({'b.c._id': req.params.c_id}, function(err, a){
    console.log(a);
});

但我不知道如何從 returnet 中獲取我需要的僅 c 對象.

But i dont know how to get from returnet a object only c object that i need.

其次如果使用 refs:

C = new Schema({
    'title': String,
});

B = new Schema({
    'title': String,
    'c': [{ type: Schema.Types.ObjectId, ref: 'C' }]
});

A = new Schema({
    'title': String,
    'b': [{ type: Schema.Types.ObjectId, ref: 'B' }]
});

如何填充所有 B、C 記錄以獲得層次結(jié)構(gòu)?

How to populate all B, C records to get hierarchy?

我試圖使用這樣的東西:

I was try to use something like this:

A
.find({})
.populate('b')
.populate('b.c')
.exec(function(err, a){
    a.forEach(function(single_a){
        console.log('- ' + single_a.title);
        single_a.b.forEach(function(single_b){
            console.log('-- ' + single_b.title);
            single_b.c.forEach(function(single_c){
                console.log('--- ' + single_c.title);
            });
        });
    });
});

但它會為 single_c.title 返回 undefined.我有辦法填充它嗎?

But it will return undefined for single_c.title. I there way to populate it?

謝謝.

推薦答案

在 Mongoose 4 中，您可以跨多個級別填充文檔:

In Mongoose 4 you can populate documents across multiple levels:

假設(shè)您有一個 User 架構(gòu)來跟蹤用戶的朋友.

Say you have a User schema which keeps track of the user's friends.

var userSchema = new Schema({
  name: String,
  friends: [{ type: ObjectId, ref: 'User' }]
});

首先populate() 讓你得到一個用戶好友列表.但是，如果您還想要用戶的朋友的朋友怎么辦?在這種情況下，您可以指定 populate 選項(xiàng)來告訴 mongoose 填充所有用戶朋友的 friends 數(shù)組:

Firstly populate() lets you get a list of user friends. But what if you also wanted a user's friends of friends? In that case, you can specify a populate option to tell mongoose to populate the friends array of all the user's friends:

User.
  findOne({ name: 'Val' }).
  populate({
    path: 'friends',
    // Get friends of friends - populate the 'friends' array for every friend
    populate: { path: 'friends' }
  });

取自:http://mongoosejs.com/docs/populate.html#deep-填充

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