无法在mongoose中聚合查询

Question

我有两个系列： 客户和设施。 facility.clientId = clients._id 我想加入对象，但找不到任何好的代码示例。 我看过查找但无法让它工作 我想要一个设施计数与facility.clientId = clients._id 所以输出如果：

    [
    {
        "_id": "1",
        "firstname": "Blue",
        "address1": "Address 1",
        "address2": "Address 2",
        "city": "Dublin",
        "count": "2",
        "__v": 0
    },
    {
        "_id": "2",
        "firstname": "Red",
        "address1": "Address 1",
        "address2": "Address 2",
        "city": "Dublin",
        "count": "1",
        "__v": 0
    },
    {
            "_id": "3",
            "firstname": "Green",
            "address1": "Address 1",
            "address2": "Address 2",
            "city": "Dublin",
            "count": "0",
            "__v": 0
    }
]

其中count是facility.clientId = clients._id

的编号

var clientsModel = require('../models/clientsModel.js');
var facilityModel = require('../models/facilityModel.js');

    list: function (req, res) {   
            clientsModel.find({}, null, {sort: '_id'}, function (err, clientss) {

                Object.keys(clientss).forEach(function(key) {
                    facilityModel.count({clientId: clientss[key]._id}, function(err, c) {
                        console.log('Count is ' + c + " key:" + key);
                        clientss[key].count = c;
                    });



                });
                return res.json(clientss);
            });
        },

我已尝试过所有功能，但无法使其正常工作，请将任何代码示例指向正确的方向，这样做会很好。

我知道有几个查询和聚合查询的例子，但我只是不让它工作。