Display all collections in mongodb+express - node.js

Question

This is my code for sending data to a database:
app.post('/thanks', function(req, res) {
if (atendees.checkin === req.body.dbstring) {
dbConn.then(client => {
delete req.body._id;
const db = client.db('mydata')
db.collection(atendees.checkin).insertOne(req.body);
})
(...)
This is how I display on the page after clicking on a href link:
app.get('/view-feedbacks', function(req, res) {
dbConn.then(client => {
const db = client.db('mydata')
db.collection(atendees.checkin).find({}).toArray().then(function(feedbacks) {
res.status(200).json(feedbacks);
atendees.checkin = ' '
}).catch(err => {
throw(err);
})
});
});
That works fine. How can I do something similar to display all collections from the database instead of just the individual ones?
This is what I tried to do:
app.get('/view-history', function(req, res) {
dbConn.then(client => {
const db = client.db('mydata')
db.listCollections().toArray().then(function(collInfos) {
res.status(200).json(collInfos);
atendees.checkin = ' '
}).catch(err => {
throw(err);
})
});
});
But it just gives me the name of each collection. I want to show all collections and all of their elements.
Edit: my question is different from this one: MongoDB Show all contents from all collections .I'm trying to do this on express.js, not on the terminal
Edit2: Using db.collection:
app.get('/view-history', function(req, res) {
dbConn.then(client => {
const db = client.db('mydata')
db.collections().then(function(feedbacks) {
res.status(200).json(feedbacks);
atendees.checkin = ' '
}).catch(err => {
throw(err);
})
});
But this gives the error: TypeError: converting circular structure to JSON

Answer 1

With async/await, this could be done:
app.get('/view-history', async (req, res) => {
try {
const client = await dbConn;
const db = client.db('mydata');
let collections = await db.collections();
let documents = await Promise.all(collections.map(async (collection) => {
let documents = await collection.find({}).toArray();
return Promise.resolve([collection.collectionName, documents]); // Retain collectionName
}));
// Format into an object that looks like `collectionName: documents`
let formatted = documents.reduce((obj, collection) => {
obj[collection[0]] = collection[1];
return obj;
}, {});
res.json(formatted);
} catch (e) {
console.error(e);
res.sendStatus(500);
}
});
A Promise-only approach:
app.get('/view-history', (req, res) => {
dbConn.then((client) => {
const db = client.db('mydata');
return db.collections();
}).then((collections) => {
return Promise.all(collections.map((collection) => {
return new Promise((resolve, reject) => {
collection.find({}).toArray().then((documents) => {
resolve([collection.collectionName, documents]);
}).catch(reject);
});
}));
}).then((documents) => {
let formatted = documents.reduce((obj, collection) => {
obj[collection[0]] = collection[1];
return obj;
}, {});
res.json(formatted);
}).catch((e) => {
console.error(e);
res.sendStatus(500);
});
});
The main reason this code is unnecessarily verbose is because instead of just returning a big array filled with arrays of documents, you probably want an object that retains the name of the collection, like so:
{
collection1: [...documents...],
collection2: [...documents...],
...
}
Instead of:
[
[...documents...],
[...documents...],
...
]
If you do want just a big array of each collection without caring about the names of the collections, it becomes much simpler:
async/await version:
app.get('/view-history', async (req, res) => {
try {
const client = await dbConn;
const db = client.db('mydata');
let collections = await db.collections();
let documents = await Promise.all(collections.map((collection) => collection.find({}).toArray()));
res.json(documents);
} catch (e) {
console.error(e);
res.sendStatus(500);
}
});
Promise-only version:
app.get('/view-history', (req, res) => {
dbConn.then((client) => {
const db = client.db('mydata');
return db.collections();
}).then((collections) => {
return Promise.all(collections.map((collection) => collection.find({}).toArray()));
}).then((documents) => {
res.json(documents);
}).catch((e) => {
console.error(e);
res.sendStatus(500);
});
});

Answer 2

Have you tried just db.collections()? If that also doesn't give what you need, you might have to invoke db.collection(<name>) on each of the names you get from listCollections.