I have 2 models like this
const Db = mongoose.model('db', dbSchema);
const Beacon = mongoose.model('beacon', dbSchema2);
Now I want to export them. First I export Db and everything is fine. I can do an HTTP request with it.
module.exports = Db;
However, when I try to export ´the 2nd one outside, it stops functioning. The functions below will return a blank JSON file as a response.
module.exports = Db;
module.exports = Beacon;
This won't work either. It returns an error handler saying all my functions in the handler is not function.
module.exports = {
Db, Beacon
}
This is the function on the file I import the models.
router.get('/data/:id', function(req, res, next) {
Db.findOne({ _id: req.params.id }).then(function(db) {
res.send(db);
});
}
The return from the handler is Db.findOne is not a function.
Is there any way to export them both? Thank you.
Here is the importing on another file
const Db = require('./db.js');
const Beacon = require('.db.js');
This should work:
Exporting in one file
module.exports = { Db, Beacon };
Then, importing in another file
const { Db, Beacon } = require('path-to-db.js');
// use them
Db.doSomething();
Beacon.doSomethingElse();
Notice that this uses the ECMAS 6 Destructuring Assignment (additional info on MDN)
Related
I'm reading the book introducing NodeJS with a simple web application example. The requirement in the example is that there are several data store classes in its own module, and we need to adopt the data store dynamically by setting environment variable. The code snippets of the example is something like following:
// memory-store.mjs
// The data store for storing data in memory
export default class MemoryStore {
// Some CRUD operation
}
// fs-store.mjs
// The data store for storing data into file system
export default class FSStore {
// Some CRUD operation
}
// store.mjs
// Provide a async function to import data store dynamically and
// set the instance to variable store, which is exported
let store;
async function load() {
try {
const moduleName = process.env.MODULE_NAME ?? 'memory';
const storeModule = await import(`./${moduleName}-store.mjs`);
const storeClass = storeModule.default;
store = new storeClass();
return store;
} catch(err) {
throw new Error('Something goes wrong...');
}
}
export { load, store };
// app.mjs
// Import the function to load the data store dynamically and
// the exported store for fetching data list
import express from 'express';
import { load, store } from './store.mjs';
const app = express();
load()
.then(store => {})
.catch(err => console.error(`Exception with error: ${err}`));
app.use('/', (req, res, next) => {
const dataList = store.retrieveAll();
res.send(dataList);
});
The code snippets above is not same as the one in the book overall. But the concept is same. It works fine in my local environment, but I'm wondering isn't there any problem if the request is coming and handled before the data store is imported due that the import function is async operation? Are there other solutions which can fulfill the requirement? Or I'm just missing something that the example from the book is just masterpiece? Thanks in advance!
If you want to guarantee that store has been initialized before any requests are handled by your express app, you could set up the express listener after the load promise has resolved. This would be as simple as the following:
import express from 'express';
import { load, store } from './store.mjs';
const app = express();
app.use('/', (req, res, next) => {
const dataList = store.retrieveAll();
res.send(dataList);
});
load()
.then(() => {
app.listen(port, () => {
console.log(`Example app listening at http://localhost:${port}`);
});
})
.catch(err => console.error(`Exception with error: ${err}`));
I'm using Node.js to build a web application.
I have two files. Server.js - where I call the server to go online etc. And the other one is a file which includes a big object with data. I imported the file with data into server.js, I get the object in postman when I set the website to be live. But I can't dive inside the object to get the data inside the object. The error I'm getting says that the variable where my data is stored is not defined.
I think the fix is to import albumsData variable into server.js, but im completely stuck and can't find how to do it. If anyone has any idea, please share.
albumsData.js
const express = require('express');
const router = express.Router();
let albumsData = {
filled with data
}
router.get('/albumData', (req, res) => {
res.send(albumsData);
});
module.exports = router;
Server.js
app.use(require('./api/albumData/unikkatilData'))
app.use((req, res) => {
res.status(404)
.send(albumsData)
});
app.listen(4000, () => {
console.log('hello worldd')
})
If you want the albumsData object then you can do it like this:
In you albumsData.js file:
const albumsData = {
// Bunch of data
}
module.exports = albumsData
Then in your server.js file:
const albumData = require('./api/albumsData') // Make sure this path points directly to the albumsData.js file
move enter code here to new file (ex utils.js)
and export it exports.albumsData = albumsData; then you can call it
with const utils = require('./utils') ; utils.albumsData
I am using Node and Express with the the mssql npm package to connect to an SQL Server database. I do this in my app.js file which sets up a global variable to create a connectionPool to the database like so (I omitted some boilerplate stuff for brevity):
const mssql = require('mssql/msnodesqlv8'); // needs to use msnodesqlv8 driver for Windows Authentication to work
const express = require('express');
const app = express();
const DB_MYDB_Config = {
server: "localhost",
database: "MYDB",
options: {
trustedConnection: true // Windows auth enabled hence no username/password required
}
};
global.MSSQL_MYDB = new mssql.ConnectionPool(DB_MYDB_Config); //connectionPool available to whole app
I have a Model file called offer.js which just does this:
async function getOffersAll() {
await MSSQL_MYDB.connect(); // connects to the database
try {
var result = await MSSQL_MYDB.request(MSSQL_MYDB).query('SELECT Top(1) * FROM [dbo].[Offer]');
return result; // returns the recordset of data
} catch (error) {
console.log(error);
} finally {
if (MSSQL_MYDB){
try {
await MSSQL_MYDB.close(); // closes the DB connection
}
catch (error) {
console.log('Error closing connection');
}
}
}
}
exports.getOffersAll = getOffersAll;
So far so good. I then have a Controller file index.js which doesn't really work (explained with comments):
var router = require('express').Router();
const Offer = require('../models/offer'); // the `offer.js` file
/* the function below works perfectly */
(async function () {
var rsOffersAll = await Offer.getOffersAll();
console.dir(rsOffersAll); // works great! recordset rsOffersAll is printed to console
})();
/* this is where it goes wrong even after commenting out the test function above */
router.get('/', async function(req, res) {
var rsOffersAll = await Offer.getOffersAll(); // this just hangs and eventually I get a login failed error for SQL Server.
console.dir(rsOffersAll);
res.render('index', { pagetitle: 'Homepage'}); // never renders
});
module.exports = router;
My question is why does the first async function() that awaits a result from Offer.getOffersAll() not fail, but the same async function placed within the router.get('/') handler fails with a login error? If I remove the var rsOffersAll = await Offer.getOffersAll(); from the router.get('/') handler then the page renders, but of course I have no data to pass to it.
The exact same thing happens even if I store the test function's value in a variable and try to put it in the router.get() handler like this:
async function getOffersTest() {
return await Offer.getOffersAll();
}
router.get('/', async function(req, res) {
var rsOffersAll = await getOffersTest(); // still breaks
console.dir(rsOffersAll);
res.render('index', { pagetitle: 'Homepage'}); // still never renders
});
My ultimate question how do I fix this so it just works the way it should in that when the homepage is visited, the router waits for the data to be returned from the database and then I can pass it to my view or just print to the console if I want?
because of this line global.MSSQL_MYDB = new mssql.ConnectionPool(DB_MYDB_Config);,
when you execute this code outside of router,
(async function () {
var rsOffersAll = await Offer.getOffersAll();
console.dir(rsOffersAll); // works great! recordset rsOffersAll is printed to console
})();
getOffersAll has access to global variable,
and you can successfully connect with db in line await MSSQL_MYDB.connect(); //
but as for router, global scope is the current module.exports object, not the global object.
Solution
you can set MSSQL_MYDB in app like this,
app.set('MSSQL_MYDB')
then you can get this same variable in following function like this
router.get('/', async function(req, res) {
const MSSQL_MYDB = req.app.get('MSSQL_MYDB')
var rsOffersAll = await getOffersTest(MSSQL_MYDB );
console.dir(rsOffersAll);
res.render('index', { pagetitle: 'Homepage'}); // still never renders
});
This whole problem was just solved and it is a bug or something in node mssql package. It only works if you provide a username and password. If you use options: {trustedConnection: true } to enable windows authentication, then the router can never log in. I don't know why this is the case, but if you just supply a username and password (I used sa for testing) then it works fine.
I have hard time understanding why my code doesn't work. I am using node package mssql and want to have database pool connection initiation in separate file:
databaseConnection.js:
const sql = require("mssql/msnodesqlv8");
config = {
database: process.env.DB_NAME,
server: process.env.DB_SERVER,
driver: "msnodesqlv8",
options: {
trustedConnection: true
}
};
let pool = sql.connect(config);
module.exports = pool;
Then I have my express route file data.js
const express = require("express");
const router = express.Router();
const db = require("../configs/databaseConnection");
router.get("/dataList", async (req, res) => {
let allData = await db.request().query("select * from dataList");
console.log(allData);
res.render("dataList", { title: "Data list" });
});
module.exports = router;
However, when I start the server and go to the route I get error:
(node:13760) UnhandledPromiseRejectionWarning: TypeError: db.request is not a function
The thing is if I setup precisely as this example mssql documentation (where verything would be done in the route) it works. However, if database connection is in separate file it doesn't work.
I would appreciate any help understanding this
Regards,
Rokas
sql.connect returns a promise, so once we know that, we can either do a .then(result => ... or use await, for example:
If you want to store the db object at startup for later I'd suggest changing the line:
const db = require("../configs/databaseConnection");
to
let db = null;
require("../configs/databaseConnection").then(pool => {
db = pool;
});
I'm kinda new to module creation and was wondering about module.exports and waiting for async functions (like a mongo connect function for example) to complete and exporting the result. The variables get properly defined using async/await in the module, but when trying to log them by requiring the module, they show up as undefined. If someone could point me in the right direction, that'd be great. Here's the code I've got so far:
// module.js
const MongoClient = require('mongodb').MongoClient
const mongo_host = '127.0.0.1'
const mongo_db = 'test'
const mongo_port = '27017';
(async module => {
var client, db
var url = `mongodb://${mongo_host}:${mongo_port}/${mongo_db}`
try {
// Use connect method to connect to the Server
client = await MongoClient.connect(url, {
useNewUrlParser: true
})
db = client.db(mongo_db)
} catch (err) {
console.error(err)
} finally {
// Exporting mongo just to test things
console.log(client) // Just to test things I tried logging the client here and it works. It doesn't show 'undefined' like test.js does when trying to console.log it from there
module.exports = {
client,
db
}
}
})(module)
And here's the js that requires the module
// test.js
const {client} = require('./module')
console.log(client) // Logs 'undefined'
I'm fairly familiar with js and am still actively learning and looking into things like async/await and like features, but yeah... I can't really figure that one out
You have to export synchronously, so its impossible to export client and db directly. However you could export a Promise that resolves to client and db:
module.exports = (async function() {
const client = await MongoClient.connect(url, {
useNewUrlParser: true
});
const db = client.db(mongo_db);
return { client, db };
})();
So then you can import it as:
const {client, db} = await require("yourmodule");
(that has to be in an async function itself)
PS: console.error(err) is not a proper error handler, if you cant handle the error just crash
the solution provided above by #Jonas Wilms is working but requires to call requires in an async function each time we want to reuse the connection. an alternative way is to use a callback function to return the mongoDB client object.
mongo.js:
const MongoClient = require('mongodb').MongoClient;
const uri = "mongodb+srv://<user>:<pwd>#<host and port>?retryWrites=true";
const mongoClient = async function(cb) {
const client = await MongoClient.connect(uri, {
useNewUrlParser: true
});
cb(client);
};
module.exports = {mongoClient}
then we can use mongoClient method in a diffrent file(express route or any other js file).
app.js:
var client;
const mongo = require('path to mongo.js');
mongo.mongoClient((connection) => {
client = connection;
});
//declare express app and listen....
//simple post reuest to store a student..
app.post('/', async (req, res, next) => {
const newStudent = {
name: req.body.name,
description: req.body.description,
studentId: req.body.studetId,
image: req.body.image
};
try
{
await client.db('university').collection('students').insertOne({newStudent});
}
catch(err)
{
console.log(err);
return res.status(500).json({ error: err});
}
return res.status(201).json({ message: 'Student added'});
};