在model层做转换，如下：

/**

     * The attributes that should be cast to native types.

     *

     * @var array

     */

    protected $casts = ['id' => 'integer', 'category_id' => 'integer', 'version_code' => 'integer', 'valuedomain_id' => 'integer','effective_date' => 'datetime:Y-m-d','expiration_date' => 'datetime:Y-m-d'];

如代码中的effective_date