My Village模型;
<?php
namespace App;
use Illuminate'Database'Eloquent'Model;
class Village extends Model {
public function positions() {
return $this->belongsTo(Map::class, 'id', 'field_id');
}
}
My Map类迁移;
Schema::create('map_data', function (Blueprint $table) {
$table->increments('id');
$table->integer('field_type');
$table->integer('field_id');
$table->string('x');
$table->string('y');
$table->timestamps();
});
我的"villages"方法在" villagcontroller "类上;
public function villages() {
$villages = Village::with([
'positions' => function ($query) {
$query->select('x', 'y');
}
])->get();
return $villages;
}
结果;
{
"villages": [
{
"id": 1,
"name": "village 1",
"created_at": "2016-10-26 18:36:34",
"updated_at": "2016-10-26 18:36:34",
"positions": null
},
{
"id": 2,
"name": "village 2",
"created_at": "2016-10-26 18:36:34",
"updated_at": "2016-10-26 18:36:34",
"positions": null
}
]
}
只需要提到"Select"方法，而不需要提到列返回NULL。
如果我删除$query->select('x', 'y');代码，返回以下结果:
{
"villages": [
{
"id": 1,
"name": "village 1",
"created_at": "2016-10-26 18:36:34",
"updated_at": "2016-10-26 18:36:34",
"positions": {
"id": 1,
"field_type": "1",
"field_id": "1",
"x": "21",
"y": "21",
"created_at": "2016-10-26 18:36:34",
"updated_at": "2016-10-26 18:36:34"
}
},
{
"id": 2,
"name": "village 2",
"created_at": "2016-10-26 18:36:34",
"updated_at": "2016-10-26 18:36:34",
"positions": {
"id": 2,
"field_type": "1",
"field_id": "2",
"x": "0",
"y": "0",
"created_at": "2016-10-26 18:36:34",
"updated_at": "2016-10-26 18:36:34"
}
}
]
}
但是我使用$query->select('x');代码，结果应该是以下
资源:https://stackoverflow.com/a/32185643/3287225
当您尝试急切加载位置关系
村庄时Village::with(['positions'])->get();
发生了三件事:
- Eloquent加载所有村庄
- Eloquent加载所有位置
- Eloquent使用field_id列为相应的Village对象分配位置
为了使它工作，获取的位置需要有field_id列被获取，否则Eloquent无法将它们与相应的村庄匹配。
当你这样做
$query->select('x', 'y');
你只从你的位置表中获取x和y列。field_id列没有被获取，这就是为什么Eloquent无法用Village对象获取它们，这就是为什么你得到null而不是位置的集合。
代替$query->select('x', 'y');
$query->select('field_id', 'x', 'y');