Basically what I'm trying to accomplish is pulling the data from a MongoDB database and feed it into my Express.js server. Both of these are ran on the localhost with different addresses. I have tried numerous different methods to get it working and can't seem to get it to work.
Express portion
app.get('/products', function(request, response) {
var query = request.query.keywords;
var promise = new Promise(async (resolve, reject) => {
var productList = await db.getProducts(query);
resolve(productList);
});
promise.then(function(productList) {
console.log(productList); // <--- productList is undefined here
response.json({
productList
});
}).catch('Error retrieving data');
// var productList = Promise.resolve(db.getProducts(query));
// productList.then(products => response.json({products}));
});
MongoDB portion
StoreDB.prototype.getProducts = function(queryParams){
return this.connected.then(function(db){
// TODO: Implement functionality
const collection = db.collection('products');
var productList;
if (!queryParams){
console.log('no queryParams');
collection.find({}).toArray(function(err, docs) {
productList = convertToObject(docs);
// console.log(productList); // <--- productList is defined here
return productList;
});
////////////
Some extra information:
- StoreDB is a functional class with only one property , connected, which is a promise that gets resolved once the connection to the database has been established
- The Express.js server calls getProducts which then resolves the promise
- Within the getProducts call, productList is defined, but when it returns, the value is undefined
With this being said, I thought that by putting the getProducts within in a promise, it would wait for the function call to be complete, then resolve it. However, that is not the case. Some insights would be greatly appreciated. Thanks.
SOLVED
Thanks to #Renan Le Caro
app.get('/products', function(request, response, next) {
db
.getProducts(request.query.keywords)
.then(productList=>response.json({productList}))
.catch(err=>next(err));
});
StoreDB.prototype.getProducts = function(queryParams){
return this.connected.then(db =>
new Promise((resolve, reject) => {
db
.collection('products')
.find({})
.toArray((err, docs) => err ? reject(err) : resolve(docs))
})
}
getProducts is already a Promise; you shouldn't need to be wrapping a Promise in another Promise, and that just opens the code up to more places things can go wrong. But Promise.resolve does not wait for a Promise to resolve; instead, it IMMEDIATELY returns a new Promise that has already resolved with the value you pass it. That's not what you want. And .catch takes a function to run when the Promise fails, not a string.
Your code should be as simple as this:
app.get('/products', function(request, response) {
var query = request.query.keywords;
db.getProducts(query).then(function(productList) {
console.log(productList);
response.json({
productList
});
}).catch(function() {
response.send('Error retrieving data');
});
});
Or, if you prefer the async/await syntax:
app.get('/products', async function(request, response) {
var query = request.query.keywords;
try {
const productList = await db.getProducts(query);
console.log(productList);
response.json({
productList
});
} catch (err) {
response.send('Error retrieving data');
}
});
This is just a promises misuse problem. Here's a fix (not tested).
app.get('/products', function(request, response, next) {
db
.getProducts(request.query.keywords)
.then(productList=>response.json({productList}))
.catch(err=>next(err));
});
StoreDB.prototype.getProducts = function(queryParams){
return this.connected.then(db =>
new Promise((resolve, reject) => {
db
.collection('products')
.find({})
.toArray((err, docs) => err ? reject(err) : resolve(docs))
})
}
Related
I just started to play with the firebase cloud function and firestore but when I'm using firestore inside the firebase cloud function (as below code) it's return and QuerySnapshot instead of return data. If anyone has got this issue before and solved it already then tell me. It would help me to resolve this issue too.
Thanks.
export async function allRestaurants(req: Request, res: Response) {
try {
// const { id } = req.params
const restaurantsRef = admin.firestore().collection('restaurants');
const snapshot = await restaurantsRef.get();
console.log(">>>>>>>>>", snapshot);
return res.status(200).send({ data: { restaurants: snapshot } })
} catch (err) {
return handleError(res, err)
}
}
It is normal that you get a QuerySnapshot, since the get() method returns a Promise that resolves with a QuerySnapshot.
It's up to you to generate the content you want to send back to the Cloud Function consumer.
For example, you can use the forEach() method to loop over the QuerySnapshot, or, as shown below, use the docs array.
export async function allRestaurants(req: Request, res: Response) {
try {
// const { id } = req.params
const restaurantsRef = admin.firestore().collection('restaurants');
const snapshot = await restaurantsRef.get();
const responseContent = snapshot.docs.map(doc => doc.data());
return res.status(200).send({ data: { restaurants: responseContent } })
} catch (err) {
return handleError(res, err)
}
}
Ok, so I know how to program in C# fairly well and I have started programming in JS recently (node js). To be honest I was in a bot of shock from async calls.
Let's say I have this code in C#:
var t_1 = SomeAsyncTask();
var t_2 = SomeOtherAsyncTask();
Task.WaitAll(t_1, t_2);
var res_1 = t_1.Result;
var res_2 = t_2.Result;
Is there a JS equivalent of this? So far I have managed this:
In User.js:
var express = require("express");
var router = express.Router();
var sqlDo = require("../../js_help/DatabasReq/sqlDo.js");
router.get("/", async function(req, res){
var json = sqlDo.ExecCommand("select * from Users");
res.send(json); //json.recordset
});
module.exports = router;
In sqlDo.js:
module.exports = {
ExecCommand: function(command){
// sql and config are defined before.
sql.connect(config, function () {
var request = new sql.Request();
request.query(command, function (err, recordset) {
if (err) console.log(err)
console.log(recordset.recordset);
return recordset;
});
});
}
};
My problem is that this code is running async. I have tried putting await to different places but nothing worked. So when I start my server it returns nothing. I can tell that it is completing a call because I let it read results into console.
Thanks for any help!
Btw: I have tried googling/stackoverlow-ing,.. But I was not able to find anything that would look like C# equivalent. Is it even possible to write it like in c#? Again thanks for every answer...
To make your ExecCommand function async, you have to make it return a Promise. Read about Promises for instance here
module.exports = {
ExecCommand: function(command){
return new Promise((resolve, reject) => { //return a Promise from the function
sql.connect(config, function () {
var request = new sql.Request();
request.query(command, function (err, recordset) {
if (err) {
reject(err); //if there is an error, reject the Promise
} else {
resolve(recordset); //if no error, resolve the Promise with the result
}
});
});
});
}
};
Depending on your SQL library, it may also support promises already, instead of callbacks
module.exports = {
ExecCommand: function(command) {
return sql.connect(config)
.then(() => {
return new sql.Request().query(command);
})
}
};
or with async/await
module.exports = {
ExecCommand: async function(command) {
await sql.connect(config);
return await new sql.Request().query(command);
}
};
Then you can call this function in the requesthandler either like this
router.get("/", async function(req, res){
try {
var json = await sqlDo.ExecCommand("select * from Users");
res.send(json);
catch (err) {
console.log(err);
res.sendStatus(500);
}
});
or like this
router.get("/", function(req, res){
sqlDo.ExecCommand("select * from Users")
.then(json => { //the promise resolved
res.send(json);
})
.catch(err => { //the promise rejected
res.sendStatus(500);
console.log(err);
});
});
I prefer the second variant. But that may be just my personal opinion ...
I'm new in Node and I've watched some of the tutorials from the Net.
My main problem is how I can show the result from the route I created. Well, I'm getting the correct data using the console but when I access it through browser it doesn't show the json encoded data.
Here is my product.js:
const express = require('express');
const router = express.Router();
const connection = require('../connection');
router.get('/',(req,res)=>{
res.send(products());
})
async function products(){
// console.log(products)
return await getProducts();
}
function getProducts(){
return new Promise((resolve,reject) =>{
connection.query('SELECT brand,description from products limit 100', function (err, rows, fields) {
if (err) throw err
resolve(JSON.stringify(rows))
})
})
}
module.exports = router;
Here is the console log result : http://prntscr.com/llxgk2
Here is the result from the postman: http://prntscr.com/llxgy3
You need to consume the promise. In your case, probably with then and catch handlers:
router.get('/',(req,res)=>{
products()
.then(products => {
res.json(products);
})
.catch(error => {
// ...send error response...
});
});
Note I've used res.json to send the response. You probably want to change your resolve(JSON.stringify(rows)) to just resolve(rows) and leave what to do with the rows to the caller. (res.json will stringify for you.)
You might also look at Koa, which is from the same people who did Express, which provides first-class support for async functions as routes.
Hi I'm writing a short node.js app that sends an XMLHTTPRequest to an API each time it iterates over an array. The issue is it continues the foreach loop before the request is returned because of the async nature. I'm probably overlooking something big but I've spent the better part of this afternoon trying to rack my brain over this. I've tried using await to no avail, any solutions would be appreciated.
Thanks in advance.
NODE JS app
const mongoose = require("mongoose");
const fs = require("fs");
const ajax = require("./modules/ajax.js");
// Bring in Models
let Dictionary = require("./models/dictionary.js");
//=============================
// MongoDB connection
//=============================
// Opens connection to database "test"
mongoose.connect("mongodb://localhost/bookCompanion");
let db = mongoose.connection;
// If database test encounters an error, output error to console.
db.on("error", (err)=>{
console.console.error("Database connection failed.");
});
// Check for connection to the database once.
db.once("open", ()=>{
console.info("Connected to MongoDB database...");
fs.readFile("./words.json", "utf8", (err, data)=>{
if(err){
console.log(err);
} else {
data = JSON.parse(data);
data.forEach((word, index)=>{
let search = ajax.get(`LINK TO API?=${word}`);
search.then((response)=>{
let newWord = new Dictionary ({
Word: response.word,
phonetic: response.phonetic,
meaning: response.meaning
}).save();
console.log(response);
}).catch((err)=>{
console.log(err);
});
});
}
});
});
XMLHTTPRequest Module
// Get Request module utilising promises
const XMLHttpRequest = require("xmlhttprequest").XMLHttpRequest;
const get = (url)=>{
// This function will return a promise, promises use resolve and reject. The resolve is accessed through .then and the reject through the .catch
return new Promise((resolve, reject)=>{
// Create new XMLhttp (AJAX) Request
let xhr = new XMLHttpRequest();
// Sets up the request, setting it to a GET request, pointing to the website and setting it to asynchronous
xhr.open("GET", url , true);
//sends the request
xhr.send();
xhr.onload = ()=>{
if (xhr.status == 200){
// When loaded pass the response over to the .then method
resolve(JSON.parse(xhr.responseText));
} else {
// if error pass the status code to the .catch method for error handling
reject(xhr.statusText);
}
};
xhr.onerror = ()=>{
// if error pass the status code to the .catch method for error handling
reject(xhr.statusText && xhr.status);
};
});
};
module.exports.get = get;
You should use promise.all to wait for all the promises to complete. Promise.all takes array of promises as input ans waits till all the promises get resolved. It rejects with the reasIf you use promise.all, your code will be something like this.
const mongoose = require("mongoose");
const fs = require("fs");
const ajax = require("./modules/ajax.js");
// Bring in Models
let Dictionary = require("./models/dictionary.js");
//=============================
// MongoDB connection
//=============================
// Opens connection to database "test"
mongoose.connect("mongodb://localhost/bookCompanion");
let db = mongoose.connection;
// If database test encounters an error, output error to console.
db.on("error", (err) => {
console.console.error("Database connection failed.");
});
// Check for connection to the database once.
db.once("open", () => {
console.info("Connected to MongoDB database...");
fs.readFile("./words.json", "utf8", (err, data) => {
if (err) {
console.log(err);
} else {
data = JSON.parse(data);
var promiseArr = []
Promise.all(promiseArr.push(
new Promise((resolve, reject) => {
let search = ajax.get(`LINK TO API?=${word}`);
search.then((response) => {
let newWord = new Dictionary({
Word: response.word,
phonetic: response.phonetic,
meaning: response.meaning
}).save();
console.log(response);
resolve();
}).catch((err) => {
console.log(err);
reject();
});
})
)).then((response) => {
//whatever you want to do after completion of all the requests
})
}
});
});
It seems my code works fine when working with smaller arrays, the real issue I'm having is dealing with the blocking nature of the forEach loop and memory. The array I need to loop through composes of over 400,000+ words and the app runs out of memory before the forEach loop can finish and free up the call stack for the httprequests to resolve.
Any information on how I can create a synchronous forEach loop that doesn't block the call stack would be very appreciated.
Where should I call module.export, I assume, it's supposed to be a callback function.
But I'm confused as to where am I supposed to call the callback function.
I'm still confused with the solution, too complicated for me.
sql.connect(config, function(err) {
if (err)
console.log(err);
// create Request object
var request = new sql.Request();
// query to the database and get the records
request.query('select part_num,qty from CRM.CRM.Fishbowl_Inventory where not location = \'Shipping\'',
function(err, recordset) {
if (err)
console.log(err)
// send records as a response
var details = recordset;
});
});
module.exports = details;
Confusion:
Extremely sorry to bother you guys but I want to be sure that I'm doing no harm to our database by involving any database request through Javascript.
I'm testing directly with our production database, hence cautious
So as Max provided in his answer the following code
const connectToSql = require('./connectToSql');
connectToSql()
.then(details => {
console.log(details);
//Here I can do as much logic as I want
//And it won't affect my database or call multiple requests on my DB
})
.catch(err => {
console.log(err);
});
I can understand I'm asking super silly questions, very sorry about that.
You can't export the result of your function. You want to export a function that will return your value. Like this:
function connectToSql(config) {
return new Promise((resolve, reject) => {
sql.connect(config, function (err) {
if (err) {
console.log(err);
reject(err);
}
// create Request object
var request = new sql.Request();
// query to the database and get the records
request.query('select part_num,qty from CRM.CRM.Fishbowl_Inventory where not location = \'Shipping\'',
function (requestErr, recordset) {
if (err) {
console.log(requestErr);
reject(requestErr);
}
resolve(recordset);
});
});
});
}
module.exports = connectToSql;
Because your function is async, I returned a promise that will return your result. Also, your second error from your query is named the same as your first error from the connection. That would cause problems.
Example of how to use this:
const connectToSql = require('./connectToSql');
connectToSql()
.then(details => {
console.log(details);
})
.catch(err => {
console.log(err);
});