php - 按最新(最近)相关模型排序 [Laravel]

Question

我正在使用 Laravel 5.4，我有以下关系:

论坛hasMany线程 ( threads() )

主题 hasMany发帖 ( posts() )

主题 belongsTo用户 ( user() )

发帖 belongsTo用户 ( user() )

目前，在我的 ThreadsController@index 中我有以下几点:

public function index()
{
    $threads = $this->forum->threads()
        ->approved()
        ->withCount(['posts AS approved_replies' => function ($query) {
            $query->where('posts.approved', true)->where('posts.is_starting_thread', false);
        }])
        ->with(['posts' => function ($query) { // Posts
            $query->approved()
                ->with('user') // Author of post
                ->latest();
            }]
        )
        ->with('user') // Author of thread
        ->latest()
        ->paginate(20); 

    return view('forums.threads.index')->with([
        'forum' => $this->forum, 'threads' => $threads
    ]);
}

我的 index.blade.php应该显示 的列表线程 对于每个线程，其中将有:

它的作者(这就是为什么我有 ->with('user'))

回复数量(这就是为什么我有 >withCount(['posts AS approved_replies' => function ($query) { ... )

最新(最新)帖子及其作者的日期。这就是为什么:

    ->with(['posts' => function ($query) { // Posts
        $query->approved()
            ->with('user') // Author of post
            ->latest(); // LATEST first
        }]
    )

... 因为然后在 index.blade.php我可以通过以下方式访问每个线程的最新帖子:

@foreach ($threads as $thread) 
    {{ $thread->posts->first()->created_at; }}
    {{ $thread->posts->first()->user->username; }}
@endforeach 

这段代码的问题在于线程是按它们的 created_at 排序的。 ，不是最近的帖子。我想要实现的是按最新(最近的)帖子订购线程，但我不知道如何执行此操作。

Answer 1

这就是我要怎么做。它不是特别漂亮，但应该可以完成这项工作

$this->forum->threads()
    ->approved()
    ->join('posts', 'posts.thread_id', '=', 'threads.id')
    ->selectRaw('threads.*, MAX(posts.created_at) AS latest_post_at')
    ->groupBy('threads.id')
    ->orderByDesc('latest_post_at')
    ->withCount(['posts AS approved_replies' => function ($query) {
        $query->where('posts.approved', true)->where('posts.is_starting_thread', false);
    }])
    ->with(['posts' => function ($query) { // Posts
        $query->approved()
            ->with('user') // Author of post
            ->latest();
        }]
    )
    ->with('user')
    ->paginate(20);

它做了一个 join正如另一个答案所暗示的那样，然后 groups通过线程，使用 MAX聚合函数以保留每组帖子的最新日期。

编辑:

$this->forum->threads()
    ->approved()
    ->join('posts', 'posts.thread_id', '=', 'threads.id')
    ->select('threads.*', 'posts.created_at AS latest_post_at')
    ->whereNotExists(function ($subquery) {
        return $subquery->from('posts AS later_posts')
            ->whereRaw('later_posts.thread_id = posts.thread_id')
            ->whereRaw('later_posts.created_at > posts.created_at');
    })
    ->orderByDesc('latest_post_at')
    ->withCount(['posts AS approved_replies' => function ($query) {
        $query->where('posts.approved', true)
              ->where('posts.is_starting_thread', false);
    }])
    ->with(['posts' => function ($query) { // Posts
        $query->approved()
            ->with('user') // Author of post
            ->latest();
    }])
    ->with('user')
    ->paginate(20);