invoiceninja/app/Models/Invitation.php

<?php namespace App\Models;

use Illuminate\Database\Eloquent\SoftDeletes;

class Invitation extends EntityModel
{
    use SoftDeletes;
    protected $dates = ['deleted_at'];

    public function invoice()
    {
        return $this->belongsTo('App\Models\Invoice');
    }

    public function contact()
    {
        return $this->belongsTo('App\Models\Contact')->withTrashed();
    }

    public function user()
    {
        return $this->belongsTo('App\Models\User')->withTrashed();
    }

    public function account()
    {
        return $this->belongsTo('App\Models\Account');
    }

    public function getLink()
    {
        return SITE_URL.'/view/'.$this->invitation_key;
    }
}