Mongoose 按引用模型的字段对模型进行嵌套查询 [英] Mongoose nested query on Model by field of its referenced model

问题描述

似乎在 stackoverflow 上有很多关于此主题的问答，但我似乎无法在任何地方找到确切的答案.

It seems like there is a lot of Q/A's on this topic on stackoverflow, but I can't seem to find an exact answer anywhere.

我有什么:

我有 Company 和 Person 模型:

I have Company and Person models:

var mongoose = require('mongoose');
var PersonSchema = new mongoose.Schema{
                        name: String, 
                        lastname: String};

// company has a reference to Person
var CompanySchema = new mongoose.Schema{
                        name: String, 
                        founder: {type:Schema.ObjectId, ref:Person}};

我需要什么:

查找姓氏为Robertson"的人创立的所有公司

Find all companies that people with lastname "Robertson" have founded

我的尝试:

Company.find({'founder.id': 'Robertson'}, function(err, companies){
    console.log(companies); // getting an empty array
});

然后我认为 Person 没有被嵌入而是被引用，所以我使用 populate 来填充创始人-Person，然后尝试使用带有Robertson"姓氏的 find

Then I figured that Person is not embedded but referenced, so I used populate to populate founder-Person and then tried to use find with 'Robertson' lastname

// 1. retrieve all companies
// 2. populate their founders
// 3. find 'Robertson' lastname in populated Companies
Company.find({}).populate('founder')
       .find({'founder.lastname': 'Robertson'})
       .exec(function(err, companies) {
        console.log(companies); // getting an empty array again
    });

我仍然可以使用 Person 的 id 作为字符串查询公司.但这并不完全是我想要的，你可以理解

I still can query companies with Person's id as a String. But it's not exactly what I want as you can understand

Company.find({'founder': '525cf76f919dc8010f00000d'}, function(err, companies){
    console.log(companies); // this works
});

推荐答案

您不能在单个查询中执行此操作，因为 MongoDB 不支持连接.相反，您必须将其分解为几个步骤:

You can't do this in a single query because MongoDB doesn't support joins. Instead, you have to break it into a couple steps:

// Get the _ids of people with the last name of Robertson.
Person.find({lastname: 'Robertson'}, {_id: 1}, function(err, docs) {

    // Map the docs into an array of just the _ids
    var ids = docs.map(function(doc) { return doc._id; });

    // Get the companies whose founders are in that set.
    Company.find({founder: {$in: ids}}, function(err, docs) {
        // docs contains your answer
    });
});

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