Accessing dynamic collection in mongodb through mongoose - node.js

Question

I have been trying to access a collection that was dynamically created in the database through {$out: "Accepted"} in nodejs using mongoose. the collection was successfully created.
from the controller:
exports.accepted = async (req, res, next)=>{
await Pupil.aggregate([{$match: {status: "Accepted"}}, {$out: "Accepted" }])
**Accepted.find({}).then(result=>{
res.render('home/accepted', {results: result, pageTitle: 'accepted page'})
}).catch(error=>{
console.log(error)*emphasized text*
});**
}
I want to retrieve the documents in that 'Accepted' collection and render them to the ejs file.
the error message is:
Accepted.find({}).then(result=>{
^
ReferenceError: Accepted is not defined at exports.accepted...
can someone please help me out?
Thanks!

Answer 1

Welcome to StackOverflow #Jerevick
There are two possible cases here:
Case 1 - You don't need to write to a new collection
You just want to find documents of accepted pupils and render them in the EJS template, in which case:
A) You don't need to write your documents into a new collection, you can just get them from the result and pass them to your template.
exports.accepted = async (req, res, next) => {
try {
const result = await Pupil.aggregate([{ $match: { status: 'Accepted' } }]);
res.render('home/accepted', { results: result, pageTitle: 'accepted page' });
} catch (err) {
console.log(err);
}
};
B) You don't even need the aggregation framework, you can just do a simple find:
exports.accepted = async (req, res, next) => {
try {
const result = await Pupil.find({ status: 'Accepted' });
res.render('home/accepted', { results: result, pageTitle: 'accepted page' });
} catch (err) {
console.log(err);
}
};
Case 2 - you need to write to a new collection, and your example was just to simplify
If that's the case, it's important to emphasize the difference between mongoose and MongoDB. Mongoose is a wrapper around the native MongoDB driver to help with casting, and provide a nicer API.
When you add a new collection to the database using the $out stage, the mongoose isn't aware of it and it doesn't assign a model for it and has no idea what kind of data live there, in which case you would need to bypass mongoose and use the native MongoDB driver directly.
I highly advise against this approach, since you'd be giving up all the convenience mongoose provides, don't take this approach unless you really know what you're doing, there's probably a better solution than using the native driver directly.
exports.accepted = async (req, res, next) => {
try {
await Pupil.aggregate([{ $match: { status: 'Accepted' } }, { $out: 'Accepted' }]);
const acceptedCollection = mongoose.connection.collection('Accepted');
const result = await acceptedCollection.find({}).toArray();
res.render('home/accepted', { results: result, pageTitle: 'accepted page' });
} catch (err) {
console.log(err);
}
};
Here's a full reproduction script you can play with:
65209755.js
'use strict';
const mongoose = require('mongoose');
const { Schema } = mongoose;
const assert = require('assert');
run().catch(console.error);
async function run () {
await mongoose.connect('mongodb://localhost:27017/test', {
useNewUrlParser: true,
useUnifiedTopology: true
});
await mongoose.connection.dropDatabase();
const studentSchema = new Schema({
name: String,
status: String
});
const User = mongoose.model('User', studentSchema);
await User.insertMany([
{ name: 'Hafez1', status: 'Accepted' },
{ name: 'Hafez2', status: 'Accepted' },
{ name: 'Hafez3', status: 'Accepted' },
{ name: 'Hafez4', status: 'Rejected' },
{ name: 'Hafez5', status: 'Rejected' }
]);
await User.aggregate([
{ $match: { status: 'Accepted' } },
{ $out: 'acceptedstudents' }
]);
const db = mongoose.connection;
const acceptedStudents = await db.collection('acceptedstudents').find({}).toArray();
assert.deepStrictEqual(
acceptedStudents.map(student => student.name),
['Hafez1', 'Hafez2', 'Hafez3']
);
console.log('All assertions passed.');
}
Output
$ node 65209755.js
All assertions passed.