merge aggregation and find results in MongoDB - node.js

Question

I have this model:
const recordSchema = new Schema({
user: {
type: Schema.ObjectId,
ref: 'Person',
required: true
},
date: {
type: Date,
default: Date.now()
},
time: {
type: Date,
default: Date.now()
}
});
So, when I make a HTTP Get request I receive an array of records:
[{/*record1*/}, {/*record2*/}, ...]
The point is that I'm using aggregation to get the number of records of each user (I got that cover), but I would like merge this with the find results to receive something like this:
{
"records": [{/*record1*/}, {/*record2*/}, ...],
"stats": [
{
"_id" : ObjectId("5b6393f2a1d3de31d9547f63"),
"count" : 3.0
},
{
"_id" : ObjectId("5b5d22d8b6195d1b6a5d2574"),
"count" : 17.0
}
]
}
So, how do I get this?
Note: I'm using this for data for some charts, should I handle this on node or on the front-end?

Answer 1

This can be done in the back-end and if you're using MongoDB Server version 3.4.4 or greater in your backend, $facet aggregate pipeline should cover your needs.
Consider the following example which runs two aggregate queries in the same aggregate pipeline using $facet: one returns the records for today and the other returns the counts for each user in the collection:
let start = new Date();
start.setHours(0,0,0,0);
let end = new Date();
end.setHours(23,59,59,999);
Record.aggregate([
{ '$facet': {
'records': [
{ '$match': {
'date': {
'$gte': start,
'$lte': end
}
} }
],
'stats': [
{ '$group': {
'_id': '$user',
'count': { '$sum': 1 }
} }
]
} }
]).exec((err, results) => {
if (err) {
console.error(err);
throw new Error(err);
}
const data = results[0];
console.log(JSON.stringify(data, null, 4));
})
For MongoDB 3.2 and below
1. Using Promises
const recordsQuery = Record.find({ 'date': {
'$gte': start, // date object representing start of today
'$lte': end // date object representing end of today
} }).lean().exec();
const statsQuery = Record.aggregate([
{ '$group': {
'_id': '$user',
'count': { '$sum': 1 }
} }
]).exec();
Promise.all([ recordsQuery, statsQuery ]).then(([ recordsData, statsData ]) => {
const records = recordsData[0];
const stats = statsData[0];
const data = { records, stats };
console.log(JSON.stringify(data, null, 4));
}).catch(err => console.error(err));
2. Using async/await
(async () => {
try {
const recordsQuery = await Record.find({ 'date': {
'$gte': start, // date object representing start of today
'$lte': end // date object representing end of today
} }).lean().exec();
const statsQuery = await Record.aggregate([
{ '$group': {
'_id': '$user',
'count': { '$sum': 1 }
} }
]).exec();
const records = recordsQuery[0];
const stats = statsQuery[0];
const data = { records, stats };
console.log(JSON.stringify(data, null, 4));
} catch (err) {
console.error(err);
}
})();

Answer 2

You can use the $lookup operator to link the original records for the users by Id
{
$lookup:
{
from: <collection to join>,
localField: <field from the input documents>,
foreignField: <field from the documents of the "from" collection>,
as: <output array field>
}
}