laravel 使用复合主键或更改主键

laravel默认主键是id，但有时可能会须要用到复合主键，或主键不是id，那么laravel中使用Eloquent Medel如何使用呢？
代码如下：
1.只更改ID

class ParkConfig extends Model {
    protected $primaryKey = 'park_id';
}

2.复合主键
首先在app目录先建立文件 Traits/HasCompositePrimaryKey 内容如下：

namespace App\Traits;

use Illuminate\Database\Eloquent\Builder;

trait HasCompositePrimaryKey {

    /**
     * Get the value indicating whether the IDs are incrementing.
     *
     * @return bool
     */
    public function getIncrementing() {
        return false;
    }

    /**
     * Set the keys for a save update query.
     *
     * @param IlluminateDatabaseEloquentBuilder $query
     *
     * @return IlluminateDatabaseEloquentBuilder
     */
    protected function setKeysForSaveQuery(Builder $query) {
        foreach ($this->getKeyName() as $key) {
            if ($this->$key)
                $query->where($key, '=', $this->$key);
            else
                throw new Exception(__METHOD__ . 'Missing part of the primary key: ' . $key);
        }

        return $query;
    }
}

在model中使用：

use App\Traits\HasCompositePrimaryKey;

class ParkConfig extends Model {
    use HasCompositePrimaryKey;
    protected $primaryKey = ['park_id', 'key'];
}