API 在 MongoDB 中存在数据时返回空数组

Question

所有。我是一个初学者，正在尝试使用 Express 后端构建一个 React 应用程序。我已经构建了一个从 MongoDB 获取数据的 API。这是 Robo3T 显示的 MongoDB 中的数据。我的问题是数据包含似乎在 MongoDB 中显示数据的选项数组（使用 Robo3T），但选项数组在 API 响应中为空。

Data as shown by Robo3T

API 响应如下：

[
 {
   _id: "5a21536a70ef53552d30e709",
   q_text: " ¿Cuál es tu edad, sexo y lugar de nacimiento?",
   options: [ ]
 },
 {
   _id: "5a21536a70ef53552d30e70a",
   q_text: "¿Actualmente asistes a la escuela?",
   options: [ ]
 },
 {
   _id: "5a21536a70ef53552d30e70b",
   q_text: "¿Cuál es tu grado de estudios? (grado y programa)",
   options: [ ]
 }
]

Server.js

//importing all dependencies
var express = require('express');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var Question = require('./models/Question');

//Connecting to MongoDB server
mongoose.connect('mongodb://localhost/local', {useMongoClient: true});
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'MongoDB connection error'));

//Creating our Express App Instance
var app = express();
var router = express.Router();

//Specifying the port number
var port = process.env.PORT || 3001;

//Configuring body-parser
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: true}));

//To prevent errors from Cross Origin Resource Sharing, we will set our headers to allow CORS with middleware like so:
app.use(function(req, res, next) {
    res.setHeader('Access-Control-Allow-Origin', '*');
    res.setHeader('Access-Control-Allow-Credentials', 'true');
    res.setHeader('Access-Control-Allow-Methods', 'GET,HEAD,OPTIONS,POST,PUT,DELETE');
    res.setHeader('Access-Control-Allow-Headers', 'Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers');

    //and remove cacheing so we get the most recent comments
    res.setHeader('Cache-Control', 'no-cache');
    next();
});

router.get('/', function(req, res){
    res.json({message : 'API initialized'});
})

router.route('/questions')
    //retrieve all questions from database
    .get(function(req, res){
        Question.find({}, function(err, questions){
            if(err){
                res.status(500).send({error: 'Could not fetch Questions'});
            } else{
                res.json(questions);
            }
        })
    })

app.use('/api', router);

//start the server and listen for requests
app.listen(port, function(){
    console.log(`Server listening on port ${port}`);
})

models/Question.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var ObjectId = mongoose.Schema.Types.ObjectId;

var question = new Schema({
    q_text:String,
    options:[{
        type: String,
        o_text: String
    }]
});

module.exports = mongoose.model('Question',question);

从 ./components/App.jsx 访问数据

import React, {Component} from 'react';
import axios from 'axios';
import Question from './Question';

class App extends Component{
    constructor(props){
        super(props);
        this.state = {
            dataLoaded: false,
            questions: []
        };
        this.loadQuestions = this.loadQuestions.bind(this);
    }

    loadQuestions(){
        axios.get(this.props.url)
            .then(res => {
                this.setState({questions: res.data});
                this.setState({dataLoaded: true})
            })
    }

    componentDidMount(){
        this.loadQuestions();
    }

    render(){
        if(this.state.dataLoaded){
            console.log(this.state.questions[2].options);
            return(
                <div>
                    <Question text={this.state.questions[1].q_text}/>
                </div>
            )
        }
        else{
            return(
                <div>Loading...</div>
            );
        }
    }
}

export default App;

Answer 1

mongo db 中的集合名称是什么？是问题吗？默认情况下，当您在定义架构时不提供集合名称时，猫鼬会将架构名称复数，在您的情况下为 Question.您可以使用覆盖此行为 var schema = new Schema({..}, { collection: 'question' });