Mongoose sub field aggregation with full text search and project - node.js

Question

I have a Mongoose model called Session with a field named course (Course model) and I want to perform full text search on sessions with full text search, also I wanna aggregate results using fields from course sub field and to select some fields like course, date, etc.
I tried the following:
Session.aggregate(
[
{
$match: { $text: { $search: 'web' } }
},
{ $unwind: '$course' },
{
$project: {
course: '$course',
date: '$date',
address: '$address',
available: '$available'
}
},
{
$group: {
_id: { title: '$course.title', category: '$course.courseCategory', language: '$course.language' }
}
}
],
function(err, result) {
if (err) {
console.error(err);
} else {
Session.deepPopulate(result, 'course course.trainer
course.courseCategory', function(err, sessions) {
res.json(sessions);
});
}
}
);
My models:
Session
schema = new mongoose.Schema(
{
date: {
type: Date,
required: true
},
course: {
type: mongoose.Schema.Types.ObjectId,
ref: 'course',
required: true
},
palnning: {
type: [Schedule]
},
attachments: {
type: [Attachment]
},
topics: {
type: [Topic]
},
trainer: {
type: mongoose.Schema.Types.ObjectId,
ref: 'trainer'
},
trainingCompany: {
type: mongoose.Schema.Types.ObjectId,
ref: 'training-company'
},
address: {
type: Address
},
quizzes: {
type: [mongoose.Schema.Types.ObjectId],
ref: 'quiz'
},
path: {
type: String
},
limitPlaces: {
type: Number
},
status: {
type: String
},
available: {
type: Boolean,
default: true
},
createdAt: {
type: Date,
default: new Date()
},
updatedAt: {
type: Date
}
},
{
versionKey: false
}
);
Course
let schema = new mongoose.Schema(
{
title: {
type: String,
required: true
},
description: {
type: String
},
shortDescription: {
type: String
},
duration: {
type: Duration
},
slug: {
type: String
},
slugs: {
type: [String]
},
program: {
content: {
type: String
},
file: {
type: String
}
},
audience: [String],
requirements: [String],
language: {
type: String,
enum: languages
},
price: {
type: Number
},
sections: [Section],
attachments: {
type: [Attachment]
},
tags: [String],
courseCategory: {
type: mongoose.Schema.Types.ObjectId,
ref: 'course-category',
required: true
},
trainer: {
type: mongoose.Schema.Types.ObjectId,
ref: 'trainer'
},
trainingCompany: {
type: mongoose.Schema.Types.ObjectId,
ref: 'training-company'
},
status: {
type: String,
default: 'draft',
enum: courseStatus
},
path: {
type: String
},
cover: {
type: String,
required: true
},
duration: {
type: Number,
min: 1
},
createdAt: {
type: Date,
default: Date.now
},
updatedAt: {
type: Date
}
},
{ versionKey: false }
);
I am not sure if what I tried is gonna bring me what I want and I am getting this error concerning the $unwind operator:
MongoError: exception: Value at end of $unwind field path '$course'
must be an Array, but is a OID
Any kind of help will be really appreciated.

Answer 1

You can try below aggregation.
You are missing $lookup required to pull course document by joining on course object id from session document to id in the course document.
$project stage to keep the desired fields in the output.
Session.aggregate([
{
"$match": {
"$text": {
"$search": "web"
}
}
},
{
"$lookup": {
"from": "courses",
"localField": "course",
"foreignField": "_id",
"as": "course"
}
},
{
"$project": {
"course": 1,
"date": 1,
"address": 1,
"available": 1
}
}
])
Course is an array with one course document. You can use the $arrayElemAt to project the document.
"course": {"$arrayElemAt":["$course", 0]}