Laravel using avg() function with foreign key - mysql

Question

I want to get the average rates for each product.
I have a rates table which has a foreign key to product table,
the rates table is similar to this
when I try to get products with this code:
$stocks = Stocks::with('images:url,color', 'tags:tag', 'sizes', 'rates')
->get()
->pluckDistant('tags', 'tag')
->pluckDistant('sizes', 'size');
it returns this
[
{
"id": 10,
"name": "name",
"image": "1564964985mI7jTuQEZxD49SGTce6Qntl7U8QDnc8uhVxedyYN.jpeg",
"images": [
{
"url": "1564964985mI7jTuQEZxD49SGTce6Qntl7U8QDnc8uhVxedyYN.jpeg",
"color": ""
},
{
"url": "1564964985EV20c1jGvCVCzpCv2Gy9r5TnWM0hMpCBsiRbe8pI.png",
"color": ""
},
{
"url": "1564964985iFcMox6rjsUaM8CHil5oQ9HkrsDqTrqLNY1cXCRX.png",
"color": ""
}
],
"tags": [
"عطور"
],
"sizes": [],
"rates": [
{
"id": 1,
"stocks_id": 10,
"rate": 2
},
{
"id": 2,
"stocks_id": 10,
"rate": 4
}
],
}
]
How can I get the average of rates as "rates":3 using the eloquent relations to get them all by sql without php proccessing?

Answer 1

You could leverage something like Appending. Say you have a Product model which has a OneToMany relationship with Rate model.
Your Product model would look something like this:
class Product extends Model
{
protected $with = ['rates'];
protected $appends = ['average_rate'];
public function getAverageRateAttribute()
{
return $this->attributes['average_rate'] = $this->rates->avg('rate');
}
public function rates() {
return $this->hasMany(Rate::class);
}
}
Now anytime you query your products from the database, you'll have the rate appended with the result.
array:7 [▼
"id" => 1
"created_at" => "2019-08-12 14:08:09"
"updated_at" => "2019-08-12 14:08:09"
"average_rate" => 4.5
"rates" => array:2 [▶]
]
However, be aware of causing n+1 problem. If you're using this approach make sure to always eager load your rates.

Answer 2

You could just use join and use aggregate function on rates table.
Stocks::with('images:url,color', 'tags:tag', 'sizes')
->join('rates', 'rates.stocks_id', '=', 'stocks.id')
->selectRaw('stocks.*')
->selectRaw('AVG(rates.rate) as average_rating')
->selectRaw('tags.*')
->selectRaw('sizes.*')
->selectRaw('images.*')
->groupBy('stocks.id')
->get()