invoiceninja/app/Models/Expense.php

<?php namespace App\Models;

use Utils;
use DB;
use Carbon;
use Laracasts\Presenter\PresentableTrait;
use Illuminate\Database\Eloquent\SoftDeletes;
use App\Events\ExpenseWasCreated;

class Expense extends EntityModel
{
    use SoftDeletes;
    use PresentableTrait;
    
    protected $dates = ['deleted_at'];
    protected $presenter = 'App\Ninja\Presenters\ExpensePresenter';

  protected $fillable = [
        'vendor_id',
    ];    
    public function account()
    {
        return $this->belongsTo('App\Models\Account');
    }

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

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

    public function getName()
    {
        return '';
    }

    public function getEntityType()
    {
        return ENTITY_EXPENSE;
    }

    public function apply($amount)
    {
        if ($amount > $this->balance) {
            $applied = $this->balance;
            $this->balance = 0;
        } else {
            $applied = $amount;
            $this->balance = $this->balance - $amount;
        }

        $this->save();

        return $applied;
    }
}

Expense::creating(function ($expense) {
    $expense->setNullValues();
});

Expense::created(function ($expense) {
    event(new ExpenseWasCreated($expense));
});

Expense::updating(function ($expense) {
    $expense->setNullValues();
});

Expense::updated(function ($expense) {
    event(new ExpenseWasUpdated($expense));
});