Laravel Eloquent has many through variation, remove duplicates - php

Question

I've been trying to get a variation of the Laravel Eloquent 'has many through' relation working.
I have 3 models: Invoice, InvoiceLine and Order; I would like to retrieve a distinct set of all Orders of a given Invoice through its InvoiceLines.
Invoice has 1 or more InvoiceLines; InvoiceLine has exactly 1 Invoice; InvoiceLine has zero or 1 Order; Order has zero or more InvoiceLines
Below is a simplified version of the tables:
Invoice
id
InvoiceLine
invoice_id
orderid
Order
orderid
First I thought to use the default Has Many Through relationship but that won't work because my tables are different:
Then I thought to use the Many-To-Many (belongsToMany) relation:
class Invoice {
public function orders(): BelongsToMany {
return $this->belongsToMany(
Order::class,
'invoice_line',
'invoice_id',
'orderid'
);
}
}
The above code works for getting all orders, but the list is full of duplicates.
How can I setup this Invoice --> Order relation using Laravel 5.6 Eloquent ORM but have it so that the collection of Orders does not have any duplicates?
If this is not possible in a Eloquent ORM relationship definition, then how can I query these models in a different way so that I still have a relational object oriented collection of Invoices with its distinct set of related Orders?

Answer 1

Not sure if this can be done in Eloquent builder. Maybe something like this:
public function orders(): BelongsToMany {
return $this->belongsToMany(
Order::class,
'invoice_line',
'invoice_id',
'orderid'
)->distinct();
}
But you can also do:
// class Invoice
public function getRelatedOrders ()
{
$orderIdList = $this->invoiceLines->pluck('order_id')->unique();
return Order::whereIn('id', $orderIdList)->get();
{