Refactoring Laravel function to reduce number of database queries - php

Question

I wondered if anyone could offer me some advice on refactoring the below function to reduce the number of database queries? Alternatively, there may be a completely different way of achieving this using Laravel.
I am trying to calculate the P&L for a Job, which is made up of Products, which are made up of Components:
public function jobProfitAndLoss($id)
{
$products_in_job = DB::table('job_product')
->where('job_id', $id)
->get();
$total_price = 0.0000;
$total_cost = 0.0000;
foreach ($products_in_job as $row) {
$total_price = $total_price + ($row->quantity)*($row->price);
$product_id = $row->product_id;
$components_in_product = DB::table('components')
->where('product_id', $product_id)
->get();
foreach ($components_in_product as $component) {
$total_cost = $total_cost + ($component->cost)*($row->quantity);
}
}
return $total_price-$total_cost;
}
Products have Components -
https://www.dropbox.com/s/ncnij8dnh99sb9v/Screenshot%202016-04-09%2015.22.26.png?dl=0
Components belong to Products -
https://www.dropbox.com/s/3dx6u30gbod2rv4/Screenshot%202016-04-09%2015.23.43.png?dl=0
Jobs have many Products -
https://www.dropbox.com/s/q179t0knd7y8z4k/Screenshot%202016-04-09%2015.24.11.png?dl=0
You will see here that there are some of the same queries being executed multiple times, which I am not sure how to avoid in this situation -
https://www.dropbox.com/s/xonbtx9cdqvq1wd/Screenshot%202016-04-09%2015.33.07.png?dl=0
Any help is much appreciated.

Answer 1

Edit: It seems that you aren't using models. If you have not done so, create models for your database entries. You will need to use the protected $table attribute for job_product as Eloquent may not be able to automatically convert your class name into the correct table name.
First of all, set up relations if you have not done so. For example, under Job.php, include the Products relation:
public function products() {
return $this->hasMany(App\Products::class); // Assuming App is the namespace
}
Now, instead of using a Fluent query for $components_in_product, you are able to directly do $components_in_product = $products_in_job->products;. However, this still leads to N+1 queries.
As a result, take a look at this: https://laravel.com/docs/5.2/eloquent-relationships#eager-loading
$books = App\Book::with('author')->get();
foreach ($books as $book) {
echo $book->author->name;
}
For this operation, only two queries will be executed:
select * from books
select * from authors where id in (1, 2, 3, 4, 5, ...)
Therefore, change $products_in_job to an Eloquent query and add ->with('products') to the query.