Laravel Eloquent perform Aggregation function in the pivot relationship - php

Question

I would like to perform the average rating of respective product which stored in the pivot table called "reviews".Below are my existing code.
Product Model:
public function reviews(){
return $this->belongsToMany(User::class,'reviews')->withPivot('comment','rating')->withTimestamps();
}
public function getProductRatingAttribute(){
return $this->reviews()->average('rating');
}
User Model:
public function reviews(){
return $this->belongsToMany(Product::class,'reviews')->withPivot('comment','rating')->withTimestamps();
}
Migration for the reviews
Schema::create('reviews', function (Blueprint $table) {
$table->id();
$table->timestamps();
$table->unsignedBigInteger('user_id');
$table->unsignedBigInteger('product_id');
$table->string('comment')->nullable();
$table->integer('rating');
$table->foreign('user_id')->references('id')->on('users');
$table->foreign('product_id')->references('id')->on('products');
});
I have attempted to use the below to code construct the expected output but it leads N+1 issue because it does not take advantage of the eager loading of the Laravel Eloquent.
$s = Product::with('reviews')->append('product_rating');
As I check telescope, it produces 6 query which can lead performance issue when the data is large.
Expected output:
{
"msg": [
{
"id": 4,
"created_at": "2021-04-09T07:32:35.000000Z",
"updated_at": "2021-04-09T07:32:35.000000Z",
"name": "MacDonald",
"nickname": "MCD",
"users_id": 1,
"price": "0.00",
"product_rating": "3.3333",
"reviews": [
{
"id": 1,
"name": "John Smith",
"email": "john.smith#hotmail.com",
"email_verified_at": null,
"created_at": "2021-04-08T13:29:13.000000Z",
"updated_at": "2021-04-08T13:29:13.000000Z",
"role": 0,
"pivot": {
"product_id": 4,
"user_id": 1,
"comment": "Ouch",
"rating": 3,
"created_at": "2021-05-01T11:51:26.000000Z",
"updated_at": "2021-05-01T11:52:07.000000Z"
}
},
{
"id": 2,
"name": "Kelvin Ooi",
"email": "kelvin.ooi#hotmail.com",
"email_verified_at": null,
"created_at": "2021-04-08T13:29:13.000000Z",
"updated_at": "2021-04-13T12:07:11.000000Z",
"role": 1,
"pivot": {
"product_id": 4,
"user_id": 2,
"comment": "Ouch",
"rating": 5,
"created_at": "2021-05-01T11:51:26.000000Z",
"updated_at": "2021-05-01T11:52:07.000000Z"
}
},
{
"id": 1,
"name": "John Smith",
"email": "john.smith#hotmail.com",
"email_verified_at": null,
"created_at": "2021-04-08T13:29:13.000000Z",
"updated_at": "2021-04-08T13:29:13.000000Z",
"role": 0,
"pivot": {
"product_id": 4,
"user_id": 1,
"comment": "Ouch",
"rating": 2,
"created_at": "2021-05-01T11:51:26.000000Z",
"updated_at": "2021-05-01T11:52:07.000000Z"
}
}
]
},
{
"id": 10,
"created_at": null,
"updated_at": null,
"name": "Mary Bown",
"nickname": "MB",
"users_id": 1,
"price": "2.88",
"product_rating": "2.0000",
"reviews": [
{
"id": 1,
"name": "John Smith",
"email": "john.smith#hotmail.com",
"email_verified_at": null,
"created_at": "2021-04-08T13:29:13.000000Z",
"updated_at": "2021-04-08T13:29:13.000000Z",
"role": 0,
"pivot": {
"product_id": 10,
"user_id": 1,
"comment": "Ouch",
"rating": 2,
"created_at": "2021-05-01T11:51:26.000000Z",
"updated_at": "2021-05-01T11:52:07.000000Z"
}
}
]
},
{
"id": 11,
"created_at": null,
"updated_at": null,
"name": "Pizza Hut",
"nickname": "pizzahut",
"users_id": 1,
"price": "4.10",
"product_rating": null,
"reviews": [
]
},
{
"id": 12,
"created_at": "2021-04-09T08:00:42.000000Z",
"updated_at": "2021-04-09T08:00:42.000000Z",
"name": "Domino Pizza",
"nickname": "domino",
"users_id": 3,
"price": "0.00",
"product_rating": null,
"reviews": [
]
},
{
"id": 13,
"created_at": "2021-04-26T16:12:53.000000Z",
"updated_at": "2021-04-26T16:12:53.000000Z",
"name": "Chicken Chop",
"nickname": "chickchop",
"users_id": 3,
"price": "0.00",
"product_rating": null,
"reviews": [
]
}
]
}

Answer 1

Appending is performing the query on each record.
Why not perform average on the collection itself?
$s = Product::with('reviews')->get();
$avg = $s->avg('pivot.rating');
Alternatively you can modify the relationship method to include a raw select of the average rating.