Laravel Eloquent 多对多关系：在编辑表单中预选关联数据的实用指南

// app/Models/Student.php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;

class Student extends Model
{
    // ... 其他属性和方法

    /**
     * 获取学生关联的设备。
     */
    public function appliances(): BelongsToMany
    {
        return $this->belongsToMany(Appliance::class, 'dealer_appliances');
        // 'dealer_appliances' 是枢纽表名称，如果遵循Laravel命名约定，可以省略
    }

    /**
     * 获取学生关联的电话。
     */
    public function phones(): HasMany
    {
        return $this->hasMany(Phone::class);
    }
}

// app/Models/Appliance.php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;

class Appliance extends Model
{
    // ... 其他属性和方法

    /**
     * 获取拥有该设备的学生。
     */
    public function students(): BelongsToMany
    {
        return $this->belongsToMany(Student::class, 'dealer_appliances');
    }
}

// app/Http/Controllers/StudentController.php
namespace App\Http\Controllers;

use App\Models\Student;
use App\Models\Appliance;
use Illuminate\View\View;

class StudentController extends Controller
{
    /**
     * 显示编辑学生资料的表单。
     */
    public function edit(int $id): View
    {
        // 1. 获取要编辑的学生实例，并预加载其关联的设备
        $student = Student::with('appliances')->findOrFail($id);

        // 2. 获取所有可用的设备列表
        $allAppliances = Appliance::all(['id', 'name']);

        // 将数据传递给视图
        return view('students.edit', compact('student', 'allAppliances'));
    }
}

<!-- resources/views/students/edit.blade.php -->
<form action="{{ route('students.update', $student->id) }}" method="POST">
    @csrf
    @method('PUT')

    <label for="appliances">选择设备:</label>
    <select name="appliances[]" id="appliances" multiple class="form-control">
        @foreach($allAppliances as $appliance)
            <option value="{{ $appliance->id }}"
                {{ in_array($appliance->id, $student->appliances->pluck('id')->toArray()) ? 'selected' : '' }}>
                {{ $appliance->name }}
            </option>
        @endforeach
    </select>

    <button type="submit">更新学生</button>
</form>

<!-- resources/views/students/edit.blade.php -->
<form action="{{ route('students.update', $student->id) }}" method="POST">
    @csrf
    @method('PUT')

    <p>选择设备:</p>
    @foreach($allAppliances as $appliance)
        <div>
            <input type="checkbox" name="appliances[]" value="{{ $appliance->id }}" id="appliance_{{ $appliance->id }}"
                {{ in_array($appliance->id, $student->appliances->pluck('id')->toArray()) ? 'checked' : '' }}>
            <label for="appliance_{{ $appliance->id }}">{{ $appliance->name }}</label>
        </div>
    @endforeach

    <button type="submit">更新学生</button>
</form>