I am wondering if I can still use .catch() within an async function to catch the error instead of using a try-catch block.
The following code is from my project using MongoDB and Express:
router.get('/communities', EnsureAuthenticated, async (req, res) =>{
//Look up the user in the db + populate the community field
const userInfo = await User_DB
.findOne({ _id:req.user._id, })
.populate('communities')
.lean()
.catch(err => {
console.log(err)
res.status(500)
.json({
msg: 'DB: Error Fetching User Info',
});
// rest of the functions that take userInfo as the input
});
When using try-catch all variables will be limited to within the scope of that try-catch block.
If I need to use the userInfo as the input for other functions down the line I'll have to put everything within that try-catch block which doesn't look clean and can be confusing. Because you don't know which function does the error belongs to if there is any.
Is my understanding correct?
I apologize for the formatting. I'm doing this on my phone.
You can also make a central error handler, you can find an example here
Related
userSchema.pre('save',async function(next){
//hash the password before saving user to database
next()
})
Hey guys I'm trying to understand the concept of middleware in mongoose. Assuming that I have an userSchema that I run the pre hook on to hash the password before saving the user to the database. On the surface, as far as I understand, the above code that I have will hash the password (not the important part for this question) and then call next() to signal that the function is done. However, I am trying to understand how things work under the hood. I want to know what is next() ? Can you guys walk me through an example of how everything works together under the hood from start to end once the code get executed or somehow help me to have a better understanding of this concept? Thanks
Short : with the pre method you can register listeners for certain events of your Schemas. So pre('save', callback) will fire whenever you save a document of said Model. pre means it will execute before the event, so it can be used (for example) to hash a password before saving it to the document.
However, you have several options to define them, see below :
The combination of using an async callback function and providing the next parameter is not necessary, you can either :
use normal callback with next parameter
the next parameter is a function provided to you by mongoose to have a way out, or to tell mongoose you are done and to continue with the next step in the execution chain. Also it is possible to pass an Error to next it will stop the execution chain.
schema.pre('save', function(next) {
// do stuff
if (error) { return next(new Error("something went wrong"); }
return next(null);
});
use async callback
Here the execution chain will continue once your async callback has finished. If there is an error and you want to break/stop execution chain you just throw it
schema.pre('save', async function() {
// do stuff
await doStuff()
await doMoreStuff()
if (error) { throw new Error("something went wrong"); }
return;
});
Straight from the docs : https://mongoosejs.com/docs/middleware.html#pre
Example
const { Schema, model } = require('mongoose');
const SomeSchema = new Schema ({
name : { type : String }
});
SomeSchema.pre('save', function (next) {
console.log('pre save fired!');
return next();
});
const Some = model('Some', SomeSchema);
console.log('before create');
const doc = new Some({ name : 'test' });
doc.save((err) => {
console.log('after saved');
});
This will output
before create
pre save fired!
after saved
I'm trying to query a collection of users using Mongoose in a Node API.
The handler looks like this:
exports.getUsers = async function(req, res, next) {
try {
let users = db.User.find();
return res.status(200).json(users);
} catch(e) {
return next(e);
}
};
This returns an error that reads Converting circular structure to JSON. When I console.log() the results of db.User.find(), I get a Query object. I've checked everything else. All of my other routes are working normally.
Well...I figured it out. I'll post the answer that I discovered in case anyone else is trying to figure this out. It turns out, through a little bit more careful reading of the documentation, that the Query object that is returned has to be executed. There are two ways to execute it - with a callback function or by returning a promise (but not both). I found this page on queries in the mongoose docs helpful. My final handler looked like this.
exports.getUsers = async function(req, res, next) {
try {
db.User.find()
.then(users => {
return res.status(200).json(users);
});
} catch(e) {
return next(e);
}
};
Next time I guess I'll dig around for a few more minutes before asking.
Edit to add:
Found a second solution. Due to the use of the async function, I also was able to use following inside the try block.
let users = await db.User.find();
return res.status(200).json(users);
var express = require('express');
var app = express();
var bodyparser = require('body-parser');
var mongoose = require('mongoose');
books = require('./models/books.js');
mongoose.connect('mongodb://localhost/books');
var db = mongoose.connection;
app.get('/api/authors', function (req, res) {
books.getBooks(function (books,err) {
if(err){
throw err;
}
res.json(books);
});
});
Why we cannot use the function(err, books) as function(books, error).
I want to know what principle it violates.
When query is executed, results are passed as parameters to callback function. If If there is any error in executing the query, the error is passed as first argument and the results are passed as second parameter to the callback function. And this is how it works.
So, you can't use it interchangeably.
In your case books.getBooks(function (books,err) {.. if there is any error books will be the one containing in it. And if not, there will be results in err params.
And I assume your query is working OK and you are throwing error checking on err value that's why you see the error.
May be you are getting confused with the names of the params. Remember, they are just the variable names, results are there according to the position of variables in callback.
To answer your question on:
Why we cannot use the function(err, books) as function(books,
error).
Most npm modules follow the Continuation-passing style(CPS) design pattern, which uses:
cb(null, data) to pass on a successful result.
cb(err) to pass on an error and exit the function.
and, the function has only one outcome.
For example:
function getBooks(cb) {
let books, error;
// .... Perform the operations
// .... If all goes well store
// .... the results in books
if (books) {
cb(null, result);
} else {
error = "There was an error loading books"
cb(error)
}
}
This is not a complete example, but shows the essence of it.
TL;DR: That, my friend, is convention.
The only thing that I can think of without knowing the error is that you might want to use:
let books = mongoose.model ('Books');
And your model should be called Books.
Is it possible to include the Error message and Model so we could have some more info about the problem?
I'm trying to build a project using the Uber API and node, and was using the node-uber wrapper here: https://github.com/shernshiou/node-uber
I've been able to access the History scope with no issue, but I'm not able to get the Profile scope. Any insight into what might be wrong? Snippets below.
Thanks!
app.get('/sign-in', function (req, res) {
var url = uber.getAuthorizeUrl(['history', 'profile']);
res.redirect(url);
console.log(url);
});
app.get('/oauth/callback', function (req, res) {
var code = req.query.code
uber.authorization({ authorization_code: code },
function (err, access_token) {
req.session.uberToken = access_token
res.redirect('/my-trips');
});
});
app.get('/api/profile', function (req, res) {
uber.user.profile({access_token: req.session.uberToken}, function (err, apiResponse) {
res.send(apiResponse);
});
});
Could you please show your error message? Based on your snippet, it's hard to understand what might go wrong without making assumptions. One thing that you might check is the authorization within the callback method. More specific, this assignment:
req.session.uberToken = access_token
You're assigning the uberToken to the request, which doesn't have any effect. Modifications to the response, however, would be useful. The request property won't exist in the method scope for the GET /api/profile. Hence, accessing the profile should return a HTTP 401 (Unauthorized).
I am an absolute NodeJS beginner and want to create a simple REST-Webservice with Express and Mongoose.
Whats the best practice to handle errors of Mongoose in one central place?
When anywhere an database error occurs I want to return a Http-500-Error-Page with an error message:
if(error) {
res.writeHead(500, {'Content-Type': 'application/json'});
res.write('{error: "' + error + '"}');
res.end();
}
In the old tutorial http://blog-next-stage.learnboost.com/mongoose/ I read about an global error listener:
Mongoose.addListener('error',function(errObj,scope_of_error));
But this doesn't seem to work and I cannot find something in the official Mongoose documentation about this listener. Have I check for errors after every Mongo request?
If you're using Express, errors are typically handled either directly in your route or within an api built on top of mongoose, forwarding the error along to next.
app.get('/tickets', function (req, res, next) {
PlaneTickets.find({}, function (err, tickets) {
if (err) return next(err);
// or if no tickets are found maybe
if (0 === tickets.length) return next(new NotFoundError));
...
})
})
The NotFoundError could be sniffed in your error handler middleware to provide customized messaging.
Some abstraction is possible but you'll still require access to the next method in order to pass the error down the route chain.
PlaneTickets.search(term, next, function (tickets) {
// i don't like this b/c it hides whats going on and changes the (err, result) callback convention of node
})
As for centrally handling mongoose errors, theres not really one place to handle em all. Errors can be handled at several different levels:
connection errors are emitted on the connection your models are using, so
mongoose.connect(..);
mongoose.connection.on('error', handler);
// or if using separate connections
var conn = mongoose.createConnection(..);
conn.on('error', handler);
For typical queries/updates/removes the error is passed to your callback.
PlaneTickets.find({..}, function (err, tickets) {
if (err) ...
If you don't pass a callback the error is emitted on the Model if you are listening for it:
PlaneTickets.on('error', handler); // note the loss of access to the `next` method from the request!
ticket.save(); // no callback passed
If you do not pass a callback and are not listening to errors at the model level they will be emitted on the models connection.
The key take-away here is that you want access to next somehow to pass the error along.
hey this is the simplest way i found..
try { } catch (error) {
console.log(error);
// checking validation
if (error.name === "ValidationError") {
const message = Object.values(error.errors).map(value => value.message);
return res.status(400).json({
error: message
})
}
res.status(400).json(error.message)
}
}
just copy paste