snipe-it/app/Http/Controllers/CheckInOutRequest.php

<?php
namespace App\Http\Controllers;

use App\Exceptions\CheckoutNotAllowed;
use App\Models\Asset;
use App\Models\Location;
use App\Models\User;

trait CheckInOutRequest
{
    /**
     * Find target for checkout
     * @return SnipeModel        Target asset is being checked out to.
     */
    protected function determineCheckoutTarget()
    {
          // This item is checked out to a location
        switch(request('checkout_to_type'))
        {
            case 'location':
                return Location::findOrFail(request('assigned_location'));
            case 'asset':
                return Asset::findOrFail(request('assigned_asset'));
            case 'user':
                return User::findOrFail(request('assigned_user'));
        }
        return null;
    }

    /**
     * Update the location of the asset passed in.
     * @param  Asset $asset Asset being updated
     * @param  SnipeModel $target Target with location
     * @return Asset        Asset being updated
     */
    protected function updateAssetLocation($asset, $target)
    {
        switch(request('checkout_to_type'))
        {
            case 'location':
                $asset->location_id = $target->id;
                break;
            case 'asset':
                $asset->location_id = $target->rtd_location_id;
                // Override with the asset's location_id if it has one
                if ($target->location_id!='') {
                    $asset->location_id = $target->location_id;
                }
                break;
            case 'user':
                    $asset->location_id = $target->location_id;
                    break;
        }
        return $asset;
    }
}