Eloquent "select" method not working with using "with" method - php

Question

My Village model;
<?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 class migration;
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();
});
My "villages" methon on "VillageController" class;
public function villages() {
$villages = Village::with([
'positions' => function ($query) {
$query->select('x', 'y');
}
])->get();
return $villages;
}
Result;
{
"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
}
]
}
"Select" method only needs to be mentioned, but not the column returns NULL.
If I delete the $query->select('x', 'y'); code returns the following results.
{
"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"
}
}
]
}
But I use the $query->select('x'); code and the result should be the following
resource: https://stackoverflow.com/a/32185643/3287225

Answer 1

When you try to eagerly load positions relation for villages with
Village::with(['positions'])->get();
3 things happen:
Eloquent loads all villages
Eloquent loads all positions
Eloquent assigns positions to corresponding Village objects using the field_id column
In order for it to work, fetched positions need to have field_id column fetched, otherwise Eloquent is unable to match them with their corresponding Villages.
When you do
$query->select('x', 'y');
you're fetching only x and y columns from your positions table. field_id column is not fetched, that's why Eloquent is unable to fetch them with Village objects and that's why you're getting null in instead of a collection of positions.
Replace
$query->select('x', 'y');
with
$query->select('field_id', 'x', 'y');
to make your code work as expected.