在模型上按其引用模型的字段进行猫鼬嵌套查询

Question

关于stackoverflow的这个主题似乎有很多问题，但是我似乎在任何地方都找不到确切的答案。

我有的：

我有Company和Person模型：

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}};

我需要的：

查找姓氏为“ Robertson”的人已创建的所有公司

我试过的

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

然后我发现Person不是嵌入式的，而是被引用的，所以我使用populate来填充Founder-
Person，然后尝试使用带有’Robertson’姓氏的find

// 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
    });

我仍然可以用Person的ID作为字符串查询公司。但这不是我想要的，正如您所了解的

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

Answer 1

您无法在单个查询中执行此操作，因为MongoDB不支持联接。相反，您必须将其分为几个步骤：

// 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
    });
});