I have a schema of USERS:
const signUpTemplate = new mongoose.Schema({
fullname: {
type: String,
},
purchasedCourses: {
type: Array,
default: [] //Here courseIdList is pushed with unique ID and course name
}
});
And a schema of courses:
const courseIdList = new mongoose.Schema({
_id: { type: String },
courseName: { type: String },
purchaseDate: {
type: Date,
default: Date.now,
},
});
How can I get the total count of users having a same course? Like if a course name 'A' is purchased by 10 different users how can get this total number?
Using $lookup, you can look for the matching records of courses collection into the users collection.
db.courses.aggregate(
[{ $lookup: {
from: "users",
localField: "_id",
foreignField: "purchasedCourses._id",
as: "coursesCount"
}},
{ $addFields: { "coursesCount": { $size: "$coursesCount" } } }]
)
Read More on $lookup;