I am using NEDB for some local storage in an NodeJS Application. Therefore I do have an handlerscript "nedbhandler.js" which I do require in my main.js.
var NEDB = require('./nedbhandler.js');
async function test(){
var value = await NEDB.getValue_byID(1);
console.log(value)
}
test()
while in the nedbhandler.js is my query handled like this:
async function getValue_byID(id){
db.config.findOne({ _id: id }, function (err, doc) {
callback(doc);
});
function callback(doc) {
console.log(doc)
return doc;
}
}
exports.getValue_byID = getValue_byID;
While the console from nedbhandler.js logs the expected value, the main.js still is undefined.
What would be the best practice to load all config querys before loading next function in the main.js?
You want your getValue_byID function to return a promise
function getValue_byID(id){
return new Promise((resolve, reject) => {
db.config.findOne({ _id: id }, (err, doc) => {
err ? reject(err) : resolve(doc);
});
});
}
Note how I changed the function keyword to the more modern => syntax.
It is also considered better practice to use const and let insteadof var
There is a wrapper module for nedb, called NeDB-promises. It does more or less what I have done here, so you can use async/await instead of callbacks.
Related
I know this has been asked a lot but I can't seem to use the existing answers to get my code to work. I am trying to use mongojs to make a single query, then put the results in a global (relative to the scope) variable to avoid nesting multiple callbacks. However, I can't seem to get the code to wait for the query to end before continuing.
async function taskmaster() {
const db = mongojs(mongoUri.tasker);
let currentDoc;
const getTask = async function() {
db.tasks.findOne({'task_id': {'$in': [taskId, null]}}, function(err, doc) {
console.log(doc);
currentDoc = doc;
});
}
await getTask();
console.log(currentDoc);
// Code to process currentDoc below
}
No matter what I do, console.log(doc) shows a valid MongoDB document, yet console.log(currentDoc) shows "undefined". Thanks in advance!
Inside your async function, you use findOne method() in callback style, so it's totally normal that console.log(currentDoc) shows undefined, because it executes before
currentDoc = doc;
You can promisify the findOne method, to use it with async/await keyword.
I found a tutorial to promisfy a callback style function here, hope it help : https://flaviocopes.com/node-promisify/
--- EDIT ---
I rewrite your code when promising the findOne method, as suggested by O.Jones
async function taskmaster() {
const getTask = async (taskId) => {
return new Promise((resolve, reject) => {
db.tasks.findOne({'task_id': {'$in': [taskId, null]}}, function(err, doc) {
if(err) {
console.log("problem when retrieve data");
reject(err);
} else {
resolve(doc);
}
});
})
const db = mongojs(mongoUri.tasker);
const currentDoc = await getTask(taskId);
console.log(currentDoc);
}
I'm struggling right now with "async".
I'm starting with NestJs Framework and i need run a bunch of task on parallel.
Before, using Nodejs + Express only, i have been useing something like this
...
...
.get('/some/path', function(){
async.parallel({
todayBalance: async.apply(function (cb) {
return SomeFunction(params, cb);
}),
currentWeek: async.apply(function (cb) {
return SomeFunction2(params, cb);
}),
...
...
// more tasks
},
function (err, results) {
# some code for logic
# here i get my result and gather data and RETURN
});
});
Nowadays, using NestJs framework, i have got something like this
myservice.ts
This is a service created for doing this.
// Service Definitions
async someFunction(userBusinessId: string): Promise<any> {
// i tried to use same strategy from Async
// but nothing accuring
async.parallel({
todayBalance: async.apply(function (cb) {
return SomeFunction(params, cb);
}),
currentWeek: async.apply(function (cb) {
return SomeFunction2(params, cb);
}),
...
...
// more tasks
},
function (err, results) {
# some code for logic
# here i get my result and gather data and RETURN
# DOESNT RETURN, NEVER EVER GETS HERE
});
}
Any idea what's wrong?
Thanks for your support!
First off I made two basics mistake
1. I Forgot use cb Function
using Nodejs + Express we just made something like this
In this case I use mysql
const SomeFunction= (userBusinessId, cb) => {
cnx.connection.query(`some pretty query`,
cb // <===== use Callback here
);
};
now using Nestjs i tried(badly results) to made something like this. Ignoring cb
const SomeFunction= (userBusinessId, cb) => {
const data = await getManager().query(`some pretty query`);
return data; // <===== WRONG INSTEAD USE cb Function, using like this parallel function will never triggered
};
Instead return single data, we must trigger the cb function overloading with result
Documentation
const SomeFunction= (userBusinessId, cb) => {
...
cb(null, data); // EXECUTE LIKE THIS, this will resume the pipe. null param suppose no error
};
2. Try to return the function service value inside the Async callback
Even if you try to do something like
async list():Promise<any>{
async.parallel({
...
// more tasks
},
function (err, results) {
return data;
});
}
OR
async list():Promise<any>{
const data = await async.parallel({
...
// more tasks
},
function (err, results) {
return data;
});
return data;
}
this funtion with always return undefined. even if you remove the Funtion Type Promise<any>
For avoid this you must return a Promise like
async list():Promise<any>{
return new Promise( (resolver, reject) => {
async.parallel({
...
// more tasks
},
function (err, results) {
if(err)
reject(err);
...
resolver(results);
});
} )
}
Hope this help you too!
I need the callback function of find from Node.js mongodb 3.1.6 to be triggered before the return statement of an async function, however the return statement is called before the callback function even-though there is a wait in front.
async function(myId) {
const myObject = MyObject()
await collection.find({where: {id: myId}}, async (err, results) => {
if (err) {
logger.error('error');
}
myObject.add(results);
});
return myObject
}
I have seen some examples where instead of find(query, callback) the pattern find(query).toArray() was used. But this doesn't run at all in my case. We use Node.js mongodb 3.1.6 with loopback-connector-mongodb maybe this is related to the problem.
If mongo doesn't provide a promise-answering function, then promisify this one yourself. Neither that promise-creating wrapper nor the anonymous callback it uses should be declared async, but the caller should....
function findById(collection, myId) {
return new Promise((resolve, reject) => {
collection.find({where: {id: myId}}, (err, results) => {
(err)? reject(err): resolve(results);
});
});
}
// now callers can use the async await pattern...
async someFunction() {
try {
let myId = // ...
let collection = // ...
let results = await findById(collection, myId);
// do something with results
} catch (err) {
// error
}
}
The key idea is that collection.find with the callback isn't eligible for await, because it doesn't return a promise. The anonymous callback function you pass to it isn't an async function... it does its work right away, as soon as find calls it back. So we build a promise around mongo, then use the new async/await syntax with that promise.
I have the following Node.js javascript function:
const createOrUpdateProfile = (pProfile) => {
db.update({facebookId: pProfile.facebookId}, pProfile, {upsert:true}, function (err, profile) {
if (err) {
console.log(err);
};
console.log("profile " + profile.occupation);
return profile;
})
};
The function is called with a user profile object which is just an ordinary object with some user information. Nothing special there.
As a matter of fact the function does what i want it to do. It either finds the profile in the MongoDB database and updates it or it inserts it into the database if it's not found.
The problem is that the profile (new or updated is never returned. I guess it has something to do with the asynchronous nature of Node.
I'm already using a call back function to capture the profile but is doesn't seems to work.
what am I missing here?
EDIT:
I changed the function to look like you sugessted:
const createOrUpdateProfile = (pProfile, callback) => {
db.update({facebookId: pProfile.facebookId}, pProfile, {upsert:true}, function (err, profile) {
if (err) {
console.log(err);
};
callback(profile);
})
};
and i call it from a graphQL mutation like this:
createOrUpdateProfile: (_, { profile }) => {
Profile.createOrUpdateProfile(profile, (cbProfile) => {
// do something with the new profile
console.log(cbProfile.occupation);
})
},
but the cbProfile appears to be undefined.
Am I doing this wrong?
I will have to look into promises later. i just want to get this working first.
Kim
You can't return from an asynchronous call inside a synchronous function. Instead, you can use a callback. Like this:
const createOrUpdateProfile = (pProfile, callback) => {
db.update({facebookId: pProfile.facebookId}, pProfile, {upsert:true}, function (err, profile) {
if (err) {
console.log(err);
};
console.log("profile " + profile.occupation);
callback(profile);
})
};
Then you can call it like this:
createOrUpdateProfile(pProfile, (profile) => {
// do something with the new profile
console.log(profile);
})
If you don't want to use callbacks, then Promises are another way of achieving this functionality.
I'm new to Express framework and learning, I'm having a problem using .then. The problem is I have 2 functions and I want the first one to complete before the second to start executing. I'm exporting the modules.
var ubm = require('./userBasic');
There are 2 functions setUserData and showUserId, the showUserId must execute only after setUserData has performed its operation.
var userId = ubm.setUserData(userName,userEmail,userDOB,moment);
userId.then(ubm.showUserId(userId));
Below are the 2 functions:
module.exports = {
setUserData: function (userName,userEmail,userDOB,moment){
//Performing database activities
return userId;
}
showUserId: function (userId){
console.log(userId);
}
}
When i run it says TypeError: Cannot read property 'then' of undefined.
Like I said I'm very new and learning and was unable to figure out the solution. I did some google search and got a brief about promise, but I don't know how to implement here.
Try using promises
module.exports = {
setUserData: function(userName, userEmail, userDOB, moment) {
return new Promise(function(resolve, reject) {
//db stuff
reject(error);
resolve(userId);
});
},
showUserId: function(userId) {
console.log(userId);
};
};
So in your execution you would write
ubm.setUserData(username, usereEmail, userDOB, moment)
.then((data) => {
showUserId(data);
})
.catch((err) => {
console.log(err);
});
A couple of things to note is that in this instance you could just log data without the need for another function like
ubm.setUserData(username, usereEmail, userDOB, moment)
.then((data) => {
console.log(data);
})
.catch((err) => {
console.log(err);
});
Whatever value you pass into resolve() will be returned as well as you pass errors into reject().