How to represent averages and other aggregates in OOP? - php

Question

I have a Model called Product. Product has among other things a price, a category and a created date.
I want to show a table showing the average price and average age by category in many places. Sometimes I want just one category, sometimes everything, sometimes only products that have been in stock for more than a certain time etc.
At the moment I'm using Laravel's Query Builder to generate those numbers in my controller, then passing that to a view.
To help try to reuse it, I have this in the methods before I need it:
$product_averages_base_query = DB::table('products')
->leftJoin('categories', 'products.MakeDescription', '=', 'categories.id')
->select(
DB::raw('count(products.id) as TotalNumber'),
DB::raw('AVG(Datediff("'.date('Y-m-d').'",products.created)) as AvgDaysInStock'),
DB::raw('AVG(Price) as AvgPrice')
);
Then when for the specific use case I use:
$averages = $product_averages_base_query->where('categories.name', '=', 'Example 1')->get();
or whatever the variant is.
This feels really "wrong" because I of course end up copying this code all over the place.
How do I represent this data in a way that will let me reuse it more easily? Should I have a class? What should it be called, and what's in it?
Should I have a Model somehow?
Any advice is welcome!

Answer 1

As for the appropriate place, you could very easily use query scopes and drop everything in your model. You'd probably want to start with your base query...
public function scopeBaseQuery($query)
{
return $query->leftJoin('categories', 'products.MakeDescription', '=', 'categories.id')
->select(
DB::raw('count(products.id) as TotalNumber'),
DB::raw('AVG(Datediff("'.date('Y-m-d').'",products.created)) as AvgDaysInStock'),
DB::raw('AVG(Price) as AvgPrice')
);
}
And then continue with the category name scope...
public function scopeOfName($query, $name)
{
return $query->where('categories.name', $name);
}
Add additional scopes as you need.
Then to use this, it would be quite easy...
$averages = Product::baseQuery()->ofName('Example 1')->get();

Answer 2

One solution would be to create an Eloquent class for the model and then put the functionality into a scope.
class Product extends Eloquent {
public function scopeAveragesByCategoryName($q, $catName) {
return $q->leftJoin('categories', 'products.MakeDescription', '=', 'categories.id')
->select(DB::raw('count(products.id) as TotalNumber'),
DB::raw('AVG(Datediff("'.date('Y-m-d').'",products.created)) as AvgDaysInStock'),
DB::raw('AVG(Price) as AvgPrice'))
->where('categories.name', '=', $catName);
}
}
$products = Product::averagesByCategoryName('Example 1')->get();
var_dump($products);
Or you could just as easily put the whole thing into a function.