Laravel 5.5 - How to query notifications for follower with created_at timestamp?

问题

A user can be a follower and/or a leader. Here userA and userB (both leaders) were followed by userC (follower) at different times (see followers table below for created_at timestamp).

To illustrate the issue, I will first layout the template:

userX action (year) // template to understand issue below

userC followed userA (2016)
userA added postA/notification (2017)
userC should get notification in feed, since they followed userA a year BEFORE their post

userB added postB/notification (2018)
userC followed userB (2019)
userC should NOT get notification in feed, since they followed userB a year AFTER their post

To accomplish this, I tried this query but it does not work correctly:

$user = App\User::find(3); // follower
$leaders = $user->leaders()
                ->with(['leaderNotifications'=>function($query){
              $query->where('notifications.created_at','>','followers.created_at');
                }])
                ->get();

I think the issue is related to the created_at not being queried correctly. Here is the exact setup to see it locally:

1) DB table name/data

users

followers

notifications

2) Models

// User
<?php
namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Foundation\Auth\User as Authenticatable;
use Illuminate\Notifications\DatabaseNotification;
use Illuminate\Notifications\DatabaseNotificationCollection;

class User extends Authenticatable {
    use Notifiable;

    // Pivot Table
    public function leaders() {
      return $this->belongsToMany('App\User', ‘followers’, 'follower_id', 'leader_id')
                  ->withPivot('created_at'); // need timestamp to compare against notification timestamp
    }

    public function leaderNotifications() {
        return $this->hasMany(DatabaseNotification::class, 'leader_id')
                    ->orderBy('created_at', 'desc');
    }
}

I am trying to fetch the correct notifications for the current follower userC, meaning only the new notifications after they followed a leader, not the leader's old notifications before they were followed by the current user. It’s also worth noting that the final query should be able to paginate->(20) of these notifications at a time, since it will be tested with a million rows, so we need to ensure it's efficient/scalable and can be paginated. What would an efficient/scalable query be for this issue?

回答1:

Here is how I solved it in case it helps others:

$user = App\User::find(3); // follower
$leaders = DB::table('notifications')
             ->join('followers','followers.leader_id','=','notifications.leader_id')
             ->where('followers.follower_id', $user->id)
             ->whereRaw('notifications.created_at > followers.created_at')
             ->paginate(20);

No need for eager loading or complicating it even more. Just a simple DB query handles it!

回答2:

1) For raw query in Laravel you should using whereRaw.

2) When using with(), Laravel get data in two query , first get result of parent query and then using result for getting with() , If you want to use pivot columns of first query in with closure,you can join.

Try this :

$user = App\User::find(3); // follower
$leaders = $user
          ->leaders()
          ->with(['leaderNotifications'=>function($query) use ($user){
              $query->whereRaw('notifications.created_at > followers.created_at')
                    ->join('followers','followers.leader_id','=','notifications.leader_id')
                    ->where('followers.follower_id',$user['id']);
                 }])
            ->get();

来源：https://stackoverflow.com/questions/49764452/laravel-5-5-how-to-query-notifications-for-follower-with-created-at-timestamp