Как метод одной модели использовать в другой модели Laravel?

class Project extends Model
{
public function user()
    {
        return $this->belongsTo(User::class, 'id');
    }

public function getProjectDir()
    {
        return $this->project_dir;
    }
}

class User extends Model
{
public function project()
    {
        return $this->hasOne(Project::class, 'user_id');
    }

public function getAvatarAttribute($value)
    {	
        if(is_null($value)) {
            $avatar = '/img/admin/no-photo.jpg';
        }else{

            if(mb_strpos($value, "logo") !== false) {
                $avatar = '/storage/projects/images/'.$this->project->getProjectDir().'/'.$value;
            }else{
                $avatar = '/img/admin/'.$value;
            }
        }       

        return $avatar;
    }
}