Sum of Items field in collection of collections - laravel

Question

I'm trying to see if it's possible, but I would like to get the sum of a field in an item in a collection of collections.
I have the following in my controller:
$prefiltered_contacts = Contact::with(['donations' => function ($query) use ($request) {
$query->whereMonth('date_received', $request->month)
->whereYear('date_received', $request->year);
}])->get();
$contacts = $prefiltered_contacts ->filter(function ($contact) {
return $contact->donations->isNotEmpty();
});
My donation class has the following:
public function monetary_donations(){
return $this->hasMany('App\Payments_Distribution', 'donation_id','id');
}
Now the last part of this is that in the Payments_Distribution class, there is a field titled amount.
If I was coming directly from the Donation model, I would access the sum of the monetary donations as $donation->monetary_donations->sum('amount'); and I would receive the sum. But how would I go about doing this from the Contact model? Or is that even possible given that it would need to go through a collection of donations to get to the collection of monetary_donations? I'm trying to get a report of all Contacts donations (and monetary donations) and output a subtotal of the monetary_donations for that specific period.

Answer 1

Sum accepts a closure as the argument. So you could do something like this:
$sum = $donations->sum(function ($donation) {
return $donation->monetary_donations->sum('amount');
});
Or 1 level higher (from $contacts):
$sum = $contacts->sum(function ($contact) {
return $contact->donations->sum(function ($donation) {
return $donation->monetary_donations->sum('amount');
});
});
Edit:
I would also recommend eager loading your relationships and filtering out contacts without donations with SQL rather than collections:
$contacts = Contact::with(['donations' => function ($query) use ($request) {
$query
->with('monetary_donations')
->whereMonth('date_received', $request->month)
->whereYear('date_received', $request->year);
}])
->whereHas('donations') // Filter out those without donations with SQL
->get();