如果急切加载的值具有价值，则仅返回雄辩的结果？

Posted 2023-03-22

【中文标题】如果急切加载的值具有价值，则仅返回雄辩的结果？

【英文标题】：Only return eloquent result if eager loaded value has value?

【发布时间】：2019-03-08 03:54:29

【问题描述】：

我想做的是获取所有对话的列表，这些对话只有一个 latestMessage 并返回一个 JSON 输出。

一个对话有许多消息，但只有一条最新消息：

public function latestMessage()

    return $this->hasOne(Message::class)->latest();

用户模式

public function conversations()

    return $this->belongsToMany('App\Conversation','conversation_participants', 'user_id', 'conversation_id');
 

对话控制器

public function index()

    $user = Auth::user();

    $user_id = $user->id;

    $conversations = $user->conversations()->with(['latestMessage'

        //Gets conversations that aren't with the user signed in
        ,'participants' => function ($query) use ($user_id)
        $query->where('user_id', '!=' , $user_id);
    ])->orderBy('updated_at','desc')->take('20')->get();

    return $conversations;

【参考方案1】：

你可以试试：

$conversations = $user->conversations()
    ->has('latestMessage') // <-- limits results to conversations with a latestMessage
    ->with(['latestMessage','participants' => function ($query) use ($user_id) 
        $query->where('user_id', '!=' , $user_id);
    ])
    ->orderBy('updated_at','desc')
    ->take('20')
    ->get();

这是文档的相关部分：

https://laravel.com/docs/5.7/eloquent-relationships#querying-relationship-existence