invoiceninja/app/Http/Requests/InvoiceRequest.php

<?php namespace App\Http\Requests;

class InvoiceRequest extends EntityRequest {

    protected $entityType = ENTITY_INVOICE;

    public function entity()
    {
        $invoice = parent::entity();
        
        // eager load the invoice items
        if ($invoice && ! $invoice->relationLoaded('invoice_items')) {
            $invoice->load('invoice_items');
        }
         
        return $invoice;
    }

}