我有3张桌子，它们是：
monitoringpost
+----------------+--------------------------------+
| Column | Type |
+----------------+--------------------------------+
|id | integer |
|nama_pos | character varying(255) |
|jenis | character varying(255) |
|sungai | character varying(255) |
|desa | character varying(255) |
|kec | character varying(255) |
|kab | character varying(255) |
|didirikan_oleh | character varying(255) |
|didirikan_tahun | integer |
|ka_jenis | character varying(255) |
|ka_pasang_ta | character varying(255) |
|ka_keterangan | character varying(255) |
|south | character varying(255) |
|east | character varying(255) |
|created_at | timestamp(0) without time zone |
|updated_at | timestamp(0) without time zone |
|mapping_code | character varying(255) |
|group | character varying |
+----------------+--------------------------------+
periodic_data
+--------+-------------------+
| Column | Type |
---------+-------------------+
| id | integer |
| uom_id | integer |
| name | character varying |
+--------+-------------------+
post_data
+-------------------+-----------------------------+
| Column | Type |
+-------------------+-----------------------------+
| id | bigint |
| monitoringpost_id | integer |
| periodic_data_id | integer |
| extern_id | character varying |
| value | double precision |
| fetched_at | timestamp without time zone |
+-------------------+-----------------------------+
这些表之间的关系是monitoringpost n<->n periodic_data，monitoringpost 1<->n post_data和periodic_data 1<->n post_data。
假设我已经有了这些表的模型，如何获取插入到value的最后一个post_data？我不知道该如何处理。这是当前代码：
public function loadByType(Request $request, $type){
$posts = MonitoringPost::with('data_periodic')->where('jenis', $type)->get();
return response()->json($posts);
}
和响应：
[
{
"id": 334,
"nama_pos": "B.Tub 0",
"jenis": "PDA",
"sungai": "STB",
"desa": "",
"kec": "",
"kab": "",
"didirikan_oleh": "",
"didirikan_tahun": null,
...
"data_periodic": [] // I want this property also contain last inserted value of its periodic data
},
....
]
PS：我正在使用Laravel 5.4