请求时无法返回数据

Question

我从其他网站复制了此代码。当我在节点中执行此代码时，我不会收到任何错误或警告。数据库不会返回任何数据。

我可以使用shell获取数据。但它不会向应用程序返回任何数据。帮我解决这个问题。

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

app.use(express.static(__dirname+'/client'));
app.use(bodyParser.json());

Genre =require('./models/genre');
Book =require('./models/book');

// Connect to Mongoose
mongoose.connect('mongodb://localhost/bookstore');
var db = mongoose.connection;

app.get('/', (req, res) => {
    res.send('Please use /api/books or /api/genres');
});

app.get('/api/genres', (req, res) => {
    Genre.getGenres((err, genres) => {
        if(err){
            throw err;
        }
        res.json(genres);
    });
});

app.post('/api/genres', (req, res) => {
    var genre = req.body;
    Genre.addGenre(genre, (err, genre) => {
        if(err){
            throw err;
        }
        res.json(genre);
    });
});

app.put('/api/genres/:_id', (req, res) => {
    var id = req.params._id;
    var genre = req.body;
    Genre.updateGenre(id, genre, {}, (err, genre) => {
        if(err){
            throw err;
        }
        res.json(genre);
    });
});

app.delete('/api/genres/:_id', (req, res) => {
    var id = req.params._id;
    Genre.removeGenre(id, (err, genre) => {
        if(err){
            throw err;
        }
        res.json(genre);
    });
});

app.get('/api/books', (req, res) => {
    Book.getBooks((err, books) => {
        if(err){
            throw err;
        }
        res.json(books);
    });
});

app.get('/api/books/:_id', (req, res) => {
    Book.getBookById(req.params._id, (err, book) => {
        if(err){
            throw err;
        }
        res.json(book);
    });
});

app.post('/api/books', (req, res) => {
    var book = req.body;
    Book.addBook(book, (err, book) => {
        if(err){
            throw err;
        }
        res.json(book);
    });
});

app.put('/api/books/:_id', (req, res) => {
    var id = req.params._id;
    var book = req.body;
    Book.updateBook(id, book, {}, (err, book) => {
        if(err){
            throw err;
        }
        res.json(book);
    });
});

app.delete('/api/books/:_id', (req, res) => {
    var id = req.params._id;
    Book.removeBook(id, (err, book) => {
        if(err){
            throw err;
        }
        res.json(book);
    });
});

app.listen(3000);
console.log('Running on port 3000...');

预订模型

const mongoose = require('mongoose');

// Book Schema
const bookSchema = mongoose.Schema({
    title:{
        type: String,
        required: true
    },
    genre:{
        type: String,
        required: true
    },
    description:{
        type: String
    },
    author:{
        type: String,
        required: true
    },
    publisher:{
        type: String
    },
    pages:{
        type: String
    },
    image_url:{
        type: String
    },
    buy_url:{
        type: String
    },
    create_date:{
        type: Date,
        default: Date.now
    }
});

const Book = module.exports = mongoose.model('Book', bookSchema);

// Get Books
module.exports.getBooks = (callback, limit) => {
    Book.find(callback).limit(limit);
}

// Get Book
module.exports.getBookById = (id, callback) => {
    Book.findById(id, callback);
}

// Add Book
module.exports.addBook = (book, callback) => {
    Book.create(book, callback);
}

// Update Book
module.exports.updateBook = (id, book, options, callback) => {
    var query = {_id: id};
    var update = {
        title: book.title,
        genre: book.genre,
        description: book.description,
        author: book.author,
        publisher: book.publisher,
        pages: book.pages,
        image_url: book.image_url,
        buy_url: book.buy_url
    }
    Book.findOneAndUpdate(query, update, options, callback);
}

// Delete Book
module.exports.removeBook = (id, callback) => {
    var query = {_id: id};
    Book.remove(query, callback);
}

这是我从git repository获取此代码的代码。运行此代码时，我没有收到任何警告或错误。 Mongo服务器也在运行。我可以使用mongo shell插入删除创建数据。这不会从数据库返回任何数据。数据库路径也是正确的。我搜索了stackoverflow旧问题。我找不到答案。我向主人发送了一条消息，他还没有回复。