How to filter with aggregation and lookup in mongoose? - mongodb

Question

I am using the following code:
Appointment
.aggregate([
{
$lookup:
{
from: "users",
localField: "doctorId",
foreignField: "_id",
as: "appointment_book"
},
},
])
.then((task) => res.send(task))
.catch((error) => console.log(error));
});
and the output is:
[{
"_id": "5dfd17823a974b39d89857d0",
"userId": "5dfcff8d2c5be31b803313ee",
"doctorId": "5dfd00102c5be31b803313f0",
"dateOfAppointment": "22/12/2019",
"timeOfAppointment": "11",
"currentStatus": "Pending",
"remarks": "",
"__v": 0,
"appointment_book": [
{
"_id": "5dfd00102c5be31b803313f0",
"name": "doctor1",
"avatar": "http://localhost:4000/public/doctor-02.jpg",
"email": "doctor1#gmail.com",
"phone": "0234820",
"city": "Faridabad",
"password": "$2a$10$m/FZg5XG9tVt86FCRAc8fO0RWhcs9D.QLFIH7BQqP/wuOR7EX8OuG",
"problem": "Neurology",
"usertype": 1,
"saltSecret": "$2a$10$m/FZg5XG9tVt86FCRAc8fO",
"__v": 0
}
]
},
{
"_id": "5dfd17bf3a974b39d89857d2",
"userId": "5dfcffdb2c5be31b803313ef",
"doctorId": "5dfd00102c5be31b803313f0",
"dateOfAppointment": "23/12/2019",
"timeOfAppointment": "11",
"currentStatus": "Pending",
"remarks": "",
"__v": 0,
"appointment_book": [
{
"_id": "5dfd00102c5be31b803313f0",
"name": "doctor1",
"avatar": "http://localhost:4000/public/doctor-02.jpg",
"email": "doctor1#gmail.com",
"phone": "0234820",
"city": "Faridabad",
"password": "$2a$10$m/FZg5XG9tVt86FCRAc8fO0RWhcs9D.QLFIH7BQqP/wuOR7EX8OuG",
"problem": "Neurology",
"usertype": 1,
"saltSecret": "$2a$10$m/FZg5XG9tVt86FCRAc8fO",
"__v": 0
}
]
}
]
My requirement to get only "userid" : "5dfcffdb2c5be31b803313ef" in mongoose. How can I do this.
output should be:
{
"_id": "5dfd17bf3a974b39d89857d2",
"userId": "5dfcffdb2c5be31b803313ef",
"doctorId": "5dfd00102c5be31b803313f0",
....
"appointment_book": [
{
"_id": "5dfd00102c5be31b803313f0",
"name": "doctor1",
....
}
]
},
{
"_id": "5dfd17bf3a974b39d89857e3",
"userId": "5dfcffdb2c5be31b803313ef",
"doctorId": "5dfd00102c5be31b803313g1",
....
"appointment_book": [
{
"_id": "5dfd00102c5be31b803313ff",
"name": "doctor2",
....
}
]
},
]

Answer 1

You need to use $match as initial stage before $lookup stage in order to filter collection for the document needed & get referenced document/documents from other collection :
Appointment.aggregate([
{ $match: { "userId": "5dfcffdb2c5be31b803313ef" } },
{
$lookup:
{
from: "users",
localField: "doctorId",
foreignField: "_id",
as: "appointment_book"
},
}])
In case of userId being an ObjectId() :
const mongoose = require('mongoose');
const userId = mongoose.Types.ObjectId("5dfcffdb2c5be31b803313ef");
Appointment.aggregate([
{ $match: { "userId": userId } },
{
$lookup:
{
from: "users",
localField: "doctorId",
foreignField: "_id",
as: "appointment_book"
}
}])
Ref : $match