mongodb中另一个集合的增量字段

我创建了两个集合，一个用于企业，另一个用于员工，它们的模式如下:

var mongoose= require('mongoose');
var Enterprise= new mongoose.Schema({
	
	name:{type:String},
	email:{type:String},
	sector:{type:String},
	employees: {type:Number,default:0}
});
module.exports={
	Enterprise:Enterprise
};

var mongoose = require('mongoose');
var employee = new mongoose.Schema({
    
    enterprise:{type: String},
	name:{type:String},
	email:{type:String},
	password:{type:String},
	gender:{type:String},
});
module.exports = {
	employee:employee
};

my add employee route，

var mongoose = require('mongoose');
var q = require('q');
var employee = mongoose.model('employee');
var enterprise = mongoose.model('enterprise');
var addEmployee = function(req, res) {
    newEmployee = new employee();
    newEmployee.enterprise = req.params.enterprise;
    newEmployee.name = req.params.name;
    newEmployee.email = req.params.email;
    newEmployee.gender = req.params.gender;
    function detailSave() {
        var deferred = q.defer();
        newEmployee.save(function(err, data) {
            if (err) {
                res.send(500);
                console.log('couldnt save employee details');
                deferred.reject({errmessage: 'couldnt save employee details', err: err});
            } else {
                res.send(200);
                deferred.resolve({data: data});
            }
        });
        return deferred.promise;
    }
    function incrementEmployee(doc) {
        var deferred = q.defer();
        enterprise.findOneAndUpdate({ 'name': doc.enterprise }, { $inc: { 'employees': 1 } },
            function(err, num) {
                if (err) {
                    deferred.reject({errmessage: 'couldnt incrementEmployee', err: err});
                    res.send(500);
                    console.log('couldnt incrementEmployee');
                } else {
                    res.send(200);
                    deferred.resolve({num:num});
                }
            });
        return deferred.promise;
    }
    detailSave()
        .then(incrementEmployee)
        .then(function(success) {
            console.log('success', success);
            res.json(200, success);
        })
        .fail(function(err) {
            res.json(500, err);
        })
        .done();
};
module.exports = {
    addEmployee: addEmployee
};

问题是当我添加员工时，企业集合中的employees字段不增加