osb/app/Traits/SiteID.php

<?php

/**
 * Ensures we retrieve and save models with the correct site_id
 */
namespace App\Traits;

use Illuminate\Support\Arr;

use App\Models\Site;
use App\Models\Scopes\SiteScope;

trait SiteID
{
	/**
	 * This model is site scoped
	 */
	protected static function booted()
	{
		static::addGlobalScope(new SiteScope);
	}

	public function save(array $options = [])
	{
		if (! Arr::get($this->attributes,'site_id'))
			$this->site_id = config('site')->site_id;

		return parent::save();
	}

	public function site()
	{
		return $this->belongsTo(Site::class);
	}
}