javascript - Use nodejs to transfer database data to the front desk. There is data in the database and the connection is successful, but why is an empty array obtained?

Question

1.api.js 2.db.js 3.vue 4. Database The result is: The result obtained is an empty array, but the link and the database are both correct. Why is this? ? ?

滿天的星座 · Answer

The crux of this problem, as @cheesekun said, is that mongoose will automatically change the collection name (first parameter) in the model to plural form.

Here I give my own experimental process and provide two solutions below.

I first created a simple project based on the meaning of the topic

app.js

const express = require('express');
const app = express();

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

app.listen(3000, () => {
    console.log('Server is running!');
});

module/db.js

const mongoose = require('mongoose');

mongoose.connect('mongodb://127.0.0.1:27017/test');
mongoose.connection
    .on('connected', _ => console.log('mongodb connect successed'))
    .on('error', _ => console.log('mongodb connect failed'))
    .on('disconnected', _ => console.log('mongodb connect disconnected'));

const Schema = mongoose.Schema;
const listSchema = new Schema({
    name: String,
    age: Number
});

const List = mongoose.model('list', listSchema);

module.exports = {
    List
}

router/api.js

const express = require('express');
const db = require('../module/db');

const router = express.Router();

router.get('/list', (req, res) => {
    db.List.find((err,data)=>{
        if(err){
            console.log(err);
        }else{
            res.json(data);
        }
    });
});

module.exports = router;

Connect to mongodb through the visualization tool and insert a document under the test database list collection in advance

Problem found

Accessed directly through the browser and got the same empty array as the subject

Find the reason

Try to insert a document into the collection

Insert a piece of data

through code at the bottom of module/db.js

const list = new List({
    name: '代码创建的数据',
    age: 1
});
list.save(function (err, data) {
    console.log(data);
});

Re-running and accessing through the browser returned the data inserted through the code

At this time, you can find through the visualization tool that there is an additional collection

lists

, and the data we inserted through the code is in it

Solution

If you do not specify the collection name explicitly, mongoose will automatically change the first parameter in model() to plural form as the collection name

Provide two solutions, both specify the collection name

The first type:

Pass the third parameter to mongoose.model() to specify the collection name

const List = mongoose.model('list', listSchema,'list');

The second type:

Pass the second configuration item to Schema to specify the collection name

const listSchema = new Schema({
    name: String,
    age: Number
},{
    collection: 'list'
});

伊谢尔伦 · Answer

I bet 50 cents.
mongooseWhen defining the model, s will be automatically added to the table name, but your login and list do not add s
The database cannot be called
This is a blog I wrote before, and it is mentioned at the bottom
mongoose deep sea pit

天蓬老师 · Answer

Add console.log(data) to res.send(data) and see if there is any result

某草草 · Answer

First of all, directly check whether the xhr return value in the console has a value. If there is a value, it means that you obtained it incorrectly.

If not, it means you didn’t send the value at all, which means the problem occurs in the backend, and you can go back and check.