Populate + Aggregate in Mongoose [duplicate] - node.js

Question

This question already has answers here:
Mongoose - How to group by and populate?
(3 answers)
Closed 6 years ago.
I have two Mongoose models: one for transactions and the other one for the tags associated with them. In order to implement some reports, I need aggregate code like this:
Transaction.aggregate([
{ $unwind: '$tags' },
{
$group: {
_id: '$tags',
amount: {
$sum: '$amount'
}
}
}
])
Question
This produces output containing _id and amount. Now, I'd like to populate the other fields (e.g. name) from the model, keeping the calculated amount column. Can I do that within a simple populate?
Edit
The schemas for the models I'm describing:
var TransactionSchema = new Schema({
description: {
type: String,
trim: true
},
amount: {
type: Number,
required: 'Forneça um valor',
},
date: {
type: Date,
required: 'Forneça uma data',
default: Date.now
},
fromOfx: {
type: Boolean,
default: false
},
created: {
type: Date,
default: Date.now
},
correlated: {
type: Boolean,
default: false
},
tags: [{
type: Schema.Types.ObjectId,
ref: 'TransactionTag'
}],
correlates: [{
type: Schema.Types.ObjectId,
ref: 'Transaction'
}],
user: {
type: Schema.Types.ObjectId,
ref: 'User'
}
});
var TransactionTagSchema = new Schema({
name: {
type: String,
required: 'Forneça um nome',
trim: true
},
description: {
type: String,
trim: true
},
amount: {
type: Number
}
});

Answer 1

You can populate an aggregation after you fetched the data from the MongoDB. This will look something like this:
// Your aggregate query from your question
Transaction.aggregate([{
$unwind: '$tags'
}, {
$group: {
_id: '$tags',
amount: {
$sum: '$amount'
}
}
}])
.exec(function(err, transactions) {
// Don't forget your error handling
// The callback with your transactions
// Assuming you are having a Tag model
Tag.populate(transactions, {path: '_id'}, function(err, populatedTransactions) {
// Your populated translactions are inside populatedTransactions
});
});