Laravel5 Eloquent ORM 查询

Subject.php

<?php
namespace App\Models;

/**
* 题目表
*
* Class Subject
* @package App\Models
*/
class Subject extends BaseModel {

/**
* 数据表
*
*/
protected $table = 'subjects';

/**
* 主键
*
*/
protected $primaryKey = 'subject_id';

/**
* 关联科目类型
*
* @return \Illuminate\Database\Eloquent\Relations\BelongsTo
*/
public function subjectClass() {
return $this->belongsTo('App\Models\SubjectClass', 'class_id', 'class_id');
}
}

TestController.php

public function testOne()
{
// 特别注意 class_id，class_id 是关联字段
$data = Subject::where('subject_id', 1)->with(['subjectClass' => function($query) {
$query->select('class_id','class_name');
}])->select('class_id','subject_id')->first();
}

public function testTwo()
{
$args = ['class_id','class_name'];
$mainArgs = ['class_id', 'subject_id', 'created_at'];

$data = Subject::where('subject_id', 1)->with(['subjectClass' => function($query) use ($args, $mainArgs) {
$query->select($args);
}])->select($mainArgs)->first();
}

public function testThree()
{
$data = Subject::where('subject_id', 1)->with('subjectClass')->first();
}

public function testFour($created_at)
{
// whereHas 和 orWhereHas 允许添加自定义条件约束到关联关系条件约束，只显示 subjects 表数据
$data = Subject::where('subject_id', 1)->whereHas('subjectClass', function ($query) use ($created_at) {
$query->where('created_at', $created_at);
})->first();
}

public function testFive()
{
// 输出 SubjectClass 对象信息
$data = Subject::find(1)->subjectClass()->first();
dd($data);
}

public function testSix()
{
// 输出 SubjectClass 对象信息
$data = Subject::find(1)->subjectClass;
dd($data);
}

with

use Illuminate\Database\Eloquent\Model;

class BaseModel extends Model{
// 注意 scopeWithOnly
public function scopeWithOnly($query, $relation, Array $columns)
{
return $query->with([$relation => function ($query) use ($columns){
// 这里根据具体业务进行调整，有些表可能不含有 id 字段
$query->select(array_merge(['class_id'], $columns));
}]);
}
}

$data = Subject::where('id', '>', '10')->withOnly('subjectClass', ['class_name'])->get();