aggregate base on match in the second collection - node.js

Question

I'm using mongodb.
And I have collection Treatments and collection Patients.
I want to find all treatments that their patient.createdBy is equal to the user who asking the data.
So I tried this
const reminders = await Treatment.aggregate([
{
$lookup: {
from: 'patients',
localField: 'patientId',
foreignField: '_id',
as: 'patient'
}
},
{ $project: { reminders: 1, reminderDate: 1 } },
{ $match: { 'patient.createdBy': { $eq: req.user._id } } }
]);
According to some examples that i saw, it's should work like this.
But it's return me an empty array
If I remove the $match its return me object like this
{
"_id": "5d1e64bdc1506a00045c6a6f",
"date": "2019-07-04T00:00:00.000Z",
"visitReason": "wewwe",
"treatmentNumber": 2,
"referredBy": "wewew",
"findings": "ewewe",
"recommendations": "ewew",
"remarks": "wwewewe",
"patientId": "5cc9a50fd915120004bf2f4e",
"__v": 0,
"patient": [
{
"_id": "5cc9a50fd915120004bf2f4e",
"lastName": "לאון",
"momName": "רןת",
"age": "11",
"phone": "",
"email": "",
"createdAt": "2019-05-01T13:54:23.261Z",
"createdBy": "5cc579d71c9d44000018151f",
"__v": 0,
"firstName": "שרה",
"lastTreatment": "2019-08-02T14:20:08.957Z",
"lastTreatmentCall": true,
"lastTreatmentCallDate": "2019-08-04T15:17:35.000Z"
}
]
}
this is patient schema
const patientSchema = new mongoose.Schema({
firstName: { type: String, trim: true, required: true },
lastName: { type: String, trim: true, required: true },
momName: { type: String, trim: true },
birthday: { type: Date },
age: { type: String, trim: true },
lastAgeUpdate: { type: Date },
phone: { type: String, trim: true },
email: { type: String, trim: true },
createdAt: { type: Date, default: Date.now },
createdBy: { type: mongoose.Schema.Types.ObjectId, required: true },
lastTreatment: { type: Date },
lastTreatmentCall: { type: Boolean },
lastTreatmentCallDate: { type: Date }
});
And this is treatment schema
const treatmentSchema = new mongoose.Schema({
date: { type: Date, default: new Date().toISOString().split('T')[0] },
visitReason: { type: String, trim: true },
treatmentNumber: { type: Number, required: true },
referredBy: { type: String, trim: true },
findings: { type: String, trim: true },
recommendations: { type: String, trim: true },
remarks: { type: String, trim: true },
reminders: { type: String, trim: true },
reminderDate: { type: Date },
patientId: { type: mongoose.Schema.Types.ObjectId }
});
what I'm missing

Answer 1

You have vanished your patient field in the second last $project stage. So instead use it at the end of the pipeline. Also you need to cast your req.user._id to mongoose objectId
import mongoose from 'mongoose'
const reminders = await Treatment.aggregate([
{
$lookup: {
from: 'patients',
localField: 'patientId',
foreignField: '_id',
as: 'patient'
}
},
{ $match: { 'patient.createdBy': { $eq: mongoose.Types.ObjectId(req.user._id) } } },
{ $project: { reminders: 1, reminderDate: 1 } }
])

Answer 2

I think you can add using the pipeline, like below
const reminders = await Treatment.aggregate([
{
$lookup: {
from: 'patients',
localField: 'patientId',
foreignField: '_id',
as: 'patient',
pipeline: [{ $match: { 'age': { $eq: "100" } } }]
}
},
]);