change hasManyThrough() relation attribute name through accessor - laravel

Question

I have 3 Models
Campaign PK(id)
CampaignMedium FK(campaign_id)
AccountReceivable FK(campaign_medium_id) (has an amount column)
Controller function:
public function all()
{
return Campaign::with(['customer', 'receivedPayments'])->get();
}
In Campaign Model relationships are defined as follows:
public function customer()
{
return $this->belongsTo(Customer::class);
}
public function accountReceivable()
{
return $this->hasManyThrough(AccountReceivable::class, CampaignMedium::class);
}
public function receivedPayments()
{
return $this->accountReceivable()
->selectRaw('sum(account_receivables.amount) as total')
->groupBy('campaign_id');
}
public function getReceivedPaymentsAttribute()
{
if (!array_key_exists('receivedPayments', $this->relations)) {
$this->load('receivedPayments');
}
$relation = $this->getRelation('receivedPayments')->first();
return ($relation) ? $relation->total : 0;
}
Final Output:
{
"data": [
{
"id": 8,
"name": "example",
"image": "campaign/90375849f6c3cc6b0e542a0e3e6295b890375849f6c3cc6b0e542a0e3e6295b8.jpeg",
"amount": 10,
"description": "saddsa",
"start_at": "2019-02-12 00:00:00",
"end_at": "2019-02-12 00:00:00",
"due_at": "2019-02-12 00:00:00",
"status": "active",
"customer": {
"id": 1,
"name": "test",
"email": "info#test.com",
"image": "customer/ec812116705ff3ae85298234fe6c4e97ec812116705ff3ae85298234fe6c4e97.jpeg",
"address": "sample address"
},
"received_payments": [
{
"total": "700",
"laravel_through_key": 8
}
]
},
{
"id": 9,
"name": "example",
"image": "campaign/fff9fadc92a809513dc28134379851aafff9fadc92a809513dc28134379851aa.jpeg",
"amount": 10,
"description": "saddsa",
"start_at": "2019-02-12 00:00:00",
"end_at": "2019-02-12 00:00:00",
"due_at": "2019-02-12 00:00:00",
"status": "active",
"customer": {
"id": 1,
"name": "test",
"email": "info#test.com",
"image": "customer/ec812116705ff3ae85298234fe6c4e97ec812116705ff3ae85298234fe6c4e97.jpeg",
"address": "sample address"
},
"received_payments": []
}
]
}
summary: trying to get the sum of AccountReceivable amount attribute, which is working fine but the getReceivedPaymentsAttribute() isn't working which needs to return the total value only. also can anyone please help me to explain why laravel_through_key is added with received_payments?

Answer 1

I've never tried to use an attribute modifier to modify a relation this way. You are overriding the expected result of receivedPayments(). You might be better off to define a separate attribute like so:
public function getSumReceivedPaymentsAttribute()
{
// ...your code...
}
Now you can access the attribute using $model->sum_received_payments or always preload it using:
// model.php
protected $appends = ['sum_received_payments'];