不进入中猫鼬保存功能

我是新手到节点js和猫鼬，无法保存在猫鼬的纪录，我使用MongoDB的图集我曾尝试多种方法来调试和尝试不同的东西，但没有得到救还是不能够进入保存功能里面。所以不能够处理保存回调moongose如果尝试打在邮递员要求其没有得到它被阻塞的响应，并没有事先订立储蓄这么感谢

controller.js

const mongoose = require('mongoose');
const User = require('../models/users');


exports.registerUser = (req,res,next)=>{
    console.log(req.body);
    const user = new User({
        _id:mongoose.Types.ObjectId(),
        firstName: req.body.firstName,
        lastName: req.body.lastName,
        email: req.body.email
    });
    user.save(function(err) {
        console.log("Callback");
        if (err) { 
            console.log("error");
            res.json({message: err});
        }
        else{
            res.json({ message: 'User created' });
        }
    })
}

router.js

const mongoose = require('mongoose');
const User = require('../models/users');


exports.registerUser = (req,res,next)=>{
    console.log(req.body);
    const user = new User({
        _id:mongoose.Types.ObjectId(),
        firstName: req.body.firstName,
        lastName: req.body.lastName,
        email: req.body.email
    });
    user.save(function(err) {
        console.log("Callback");
        if (err) { 
            console.log("error");
            res.json({message: err});
        }
        else{
            res.json({ message: 'User created' });
        }
    })
}

model.js

const mongoose = require('mongoose');
const userSchema = mongoose.Schema({
    _id: mongoose.Schema.Types.ObjectId,
    firstName: {type: String, required: true},
    lastName: {type: String, required: true},
    email: {type: String, required: true}
});

module.exports = mongoose.model('User', userSchema);

app.js

const express = require('express');
const app = express();
const bodyParser = require('body-parser');
const mongoose = require('mongoose');


const userRoutes = require('./api/routes/users');
const MongoClient = require('mongodb').MongoClient;



const uri = "mongodb+srv://<connection string>/admin";
const client = new MongoClient(uri, { useNewUrlParser: true });
client.connect(err => {
});

mongoose.Promise = global.Promise;

app.use(bodyParser.urlencoded({extended: false}));
app.use(bodyParser.json());

app.use((req,res,next )=>{
    console.log(req);
    res.header("Access-Control-Allow-Origin", "*");
    if (req.method === "OPTIONS") {
        res.header("Access-Control-Allow-Methods", "PUT, POST, PATCH, DELETE, GET");
        return res.status(200).json({});
      }
      next();
});

app.use('/', userRoutes);

app.use((req,res,next)=>{
    const error = new Error('Not Found');
    error.status = 404;
    next(error);
});

app.use((error,req,res,next)=>{
    res.status(error.status || 500);
    res.json({
        error:{
            message: error.message
        }
    })
});

module.exports = app;

你肯定猫鼬使用任何连接？好像你连接到服务器mongodb模块来代替。参见如何与猫鼬连接Getting Started文档。