Laravel Blade视图访问中间表关联数据报错及ORM优化需求

我是Laravel新手，大概率犯了入门级错误。尝试在Blade视图中访问关联表数据，让关联的用户ID在下拉框中默认选中，但页面报错，目前用原生查询实现了功能，想找更优雅的ORM实现方式。

现有代码片段 #

中间表模型（_MeetingUser） #

class _MeetingUser extends Model
{
    ...
    public function meeting()
    {
        return $this->belongsToMany(Meetings::class);
    }
    public function user()
    {
        return $this->belongsToMany(Users::class);
    }
}

会议模型（Meetings） #

class Meetings extends Model
{
    ...
    public function users()
    {
        return $this->belongsToMany(Users::class, 'meeting__user');
    }
    ...
}

控制器代码 #

class MeetingController extends Controller
{
    public function edit(Request $request): View
    {
        return view('meetings.edit', [
            'meetings' => Meetings::all(),
            'secretaries' => Users::all(),
        ]);
    ...
}

报错的Blade视图代码 #

@foreach($meetings as $meeting)
    ...
    <td>
        <select name="secretaries[]" id="secretaries">
            <option value="0">Select Secretary</option>
            @foreach($secretaries as $secretary)
                <option value="{{$secretary->id}}"
                    @if($meeting->users()->id == $secretary->id)
                        selected="selected"
                    @endif
                >{{$secretary->name}}</option>
            @endforeach
        </select>
    </td>
    ...
@endforeach

报错信息 #

Undefined property: Illuminate\Database\Eloquent\Relations\BelongsToMany::$id

当前临时解决方案（原生查询） #

{{  $existing_secretary_id=DB::scalar('select users_id from meeting__user where meetings_id = ?', [$meeting->id]); }}
<td>
    <select name="secretaries[]" id="secretaries">
        <option value="0">Select Secretary</option>
        @foreach($secretaries as $secretary)
            <option value="{{$secretary->id}}"
                @if($secretary->id == $existing_secretary_id)
                    selected="selected"
                @endif
            >{{$secretary->name}}</option>
        @endforeach
    </select>
</td>

ORM优化方案 #

1. 修正中间表模型关联 #

中间表_MeetingUser的关联应该用belongsTo而非belongsToMany，因为中间表的每条记录仅属于单个会议和单个用户：

class _MeetingUser extends Model
{
    ...
    public function meeting()
    {
        return $this->belongsTo(Meetings::class);
    }
    public function user()
    {
        return $this->belongsTo(Users::class);
    }
}

2. 控制器预加载关联避免N+1查询 #

在查询会议时预加载关联的用户，减少数据库查询次数：

class MeetingController extends Controller
{
    public function edit(Request $request): View
    {
        return view('meetings.edit', [
            'meetings' => Meetings::with('users')->get(), // 用with预加载users关联
            'secretaries' => Users::all(),
        ]);
    ...
}

3. Blade视图中用关联集合判断选中状态 #

利用Eloquent集合的contains方法，直接判断当前秘书是否属于会议关联的用户：

@foreach($meetings as $meeting)
    ...
    <td>
        <select name="secretaries[]" id="secretaries">
            <option value="0">Select Secretary</option>
            @foreach($secretaries as $secretary)
                <option value="{{ $secretary->id }}" 
                    {{ $meeting->users->contains($secretary->id) ? 'selected' : '' }}
                >{{ $secretary->name }}</option>
            @endforeach
        </select>
    </td>
    ...
@endforeach

或者先提取关联用户的ID数组，用in_array判断（效果一致）：

@foreach($meetings as $meeting)
    @php
        $assignedSecretaryIds = $meeting->users->pluck('id')->toArray();
    @endphp
    ...
    <td>
        <select name="secretaries[]" id="secretaries">
            <option value="0">Select Secretary</option>
            @foreach($secretaries as $secretary)
                <option value="{{ $secretary->id }}" 
                    {{ in_array($secretary->id, $assignedSecretaryIds) ? 'selected' : '' }}
                >{{ $secretary->name }}</option>
            @endforeach
        </select>
    </td>
    ...
@endforeach

关键说明 #

• $meeting->users()返回的是关联关系对象，不是实际的用户集合，必须去掉括号用$meeting->users才能获取加载后的用户集合。
• 预加载with('users')能避免循环中重复查询数据库，提升性能。

内容的提问来源于stack exchange，提问作者Howard Owen