如何在 Laravel 中正确使用 with() 关系？

Question

我只是想澄清如何使用表中的关系。现在，我想从 employees 表中的 designation_id 获取 designation name 记录。

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use App\Models\{
    Designations,
    Positions
};

class Employees extends Model
{
    use HasFactory;

    protected $table = 'employees';

    protected $primaryKey = 'id';

    public $timestamps = true;
    
    protected $casts = [
        'designation_id' => 'array',
        'position_id' => 'array',
        'basic_pay' => 'decimal:2',
    ];

    protected $dates = ['created_at', 'updated_at'];

    protected $fillable = [
        'first_name', 
        'last_name',
        'designation_id',
        'position_id',
        'basic_pay',
    ];

    public function designations()
    {
        return $this->hasMany(Designations::class, 'id', 'designation_id');
    }

    public function positions()
    {
        return $this->hasMany(Positions::class, 'id', 'position_id');
    }
}

这是我的指定模型：

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use App\Models\Employees;

class Designations extends Model
{
    use HasFactory;

    protected $table = 'designations';

    protected $primaryKey = 'id';

    public $timestamps = true;
    
    protected $dates = ['created_at', 'updated_at'];
    
    protected $fillable = [
        'name',
        'description'
    ];

    public function employees()
    {
        return $this->belongsTo(Employees::class, 'designation_id');
    }
}

这是我的 EmployeeController.php：

<?php
namespace App\Http\Controllers;
use Illuminate\Http\Request;
use App\Models\{
    Employees,
    Designations
};

class EmployeesController extends Controller
{
    public function index()
    { 
        $employees = Employees::with('designations', 'positions')->get();
        return array_reverse($employees);     
    }
}

我检查了我的 api url，http://localhost:8000/api/employees 并收到此错误：

SQLSTATE[HY093]：无效的参数号（SQL：从designationswhereselect *代码>designations.idin (52))

Answer 1

我建议您安装phpstorm，它为您提供了功能参数的提示，并且您将不再存在此类问题。

正确格式是：

return $this->hasMany('App\Comment', 'foreign_key', 'local_key');

在您的名称模型中：

public function DesignationNames()
    {
        return $this->hasMany(\App\Models\Employees::class, 'designation_id', 'id');
    }

当您在控制器中检索它们时，您需要使用with（）方法为：

名称：

然后，要访问相关员工集合中的属性，您需要：

$名称名称名称 -

Answer 2

你的关系参数是错误的。如果

hasMany(class, foreignKey, relatedPrimaryKey)

# Employee
public function designations()
{
    return $this->hasMany(Designations::class, 'employee_id', 'id');
}

public function positions()
{
    return $this->hasMany(Positions::class, 'employee_id', 'id');
}

您渴望加载超过 1 个关系，请使用数组表示法。

此外，$employees 将是 Collection 的实例，因此您不能将其用作 array_reverse 的参数。

您可以使用集合方法来获得相同的结果，也可以使用 $employees->all() 来获取底层数组。

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use App\Models\Employees;

class EmployeesController extends Controller
{
    public function index()
    { 
        $employees = Employees::with(['designations', 'positions'])->get();

        return $employees->reverse()->values()->all();
        // OR
        return array_reverse($employees->all());
    }
}

---

假设您的表具有如下结构：

Schema::create('employees', function (Blueprint $table) {
    $table->id();
    ...    
});

Schema::create('designations', function (Blueprint $table) {
    $table->id();
    $table->foreignId('employee_id')->constained('employees');
    ...
});

Schema::create('positions', function (Blueprint $table){
    $table->id();
    $table->foreignId('employee_id')->constained('employees');
    ...
});

由于您使用的是 increments 而不是 id()，因此代码必须稍有不同。

Schema::create('employees', function (Blueprint $table) {
    $table->increments('id')->unique();
    ...    
});

Schema::create('designations', function (Blueprint $table) {
    $table->increments('id')->unique();
    $table->unsignedInteger('employee_id');
    $table->foreign('employee_id')->references('id')->on('employees');
    ...
});

Schema::create('positions', function (Blueprint $table){
    $table->increments('id')->unique();
    $table->unsignedInteger('employee_id');
    $table->foreign('employee_id')->references('id')->on('employees');
    ...
});