Delete associated notifications when deleting discussions, posts, and users. fixes #1380

src/Discussion/Discussion.php

@@ -21,6 +21,7 @@ use Flarum\Discussion\Event\Restored;
 use Flarum\Discussion\Event\Started;
 use Flarum\Event\GetModelIsPrivate;
 use Flarum\Foundation\EventGeneratorTrait;
+use Flarum\Notification\Notification;
 use Flarum\Post\MergeableInterface;
 use Flarum\Post\Post;
 use Flarum\User\User;
@@ -97,8 +98,18 @@ class Discussion extends AbstractModel
     {
         parent::boot();
 
+        static::deleting(function (Discussion $discussion) {
+            Notification::whereSubjectModel(Post::class)
+                ->whereIn('subject_id', function ($query) use ($discussion) {
+                    $query->select('id')->from('posts')->where('discussion_id', $discussion->id);
+                })
+                ->delete();
+        });
+
         static::deleted(function (Discussion $discussion) {
             $discussion->raise(new Deleted($discussion));
+
+            Notification::whereSubject($discussion)->delete();
         });
 
         static::saving(function (Discussion $discussion) {

src/Notification/Notification.php

@@ -169,6 +169,35 @@ class Notification extends AbstractModel
         });
     }
 
+    /**
+     * Scope the query to include only notifications that have the given
+     * subject.
+     *
+     * @param Builder $query
+     * @param object $model
+     */
+    public function scopeWhereSubject(Builder $query, $model)
+    {
+        $query->whereSubjectModel(get_class($model))
+            ->where('subject_id', $model->id);
+    }
+
+    /**
+     * Scope the query to include only notification types that use the given
+     * subject model.
+     *
+     * @param Builder $query
+     * @param string $class
+     */
+    public function scopeWhereSubjectModel(Builder $query, string $class)
+    {
+        $notificationTypes = array_filter(Notification::getSubjectModels(), function ($modelClass) use ($class) {
+            return $modelClass === $class or is_subclass_of($class, $modelClass);
+        });
+
+        $query->whereIn('type', array_keys($notificationTypes));
+    }
+
     /**
      * Get the type-to-subject-model map.
      *

src/Post/Post.php

@@ -17,6 +17,7 @@ use Flarum\Discussion\Discussion;
 use Flarum\Event\GetModelIsPrivate;
 use Flarum\Event\ScopeModelVisibility;
 use Flarum\Foundation\EventGeneratorTrait;
+use Flarum\Notification\Notification;
 use Flarum\Post\Event\Deleted;
 use Flarum\User\User;
 use Illuminate\Database\Eloquent\Builder;
@@ -106,6 +107,8 @@ class Post extends AbstractModel
 
         static::deleted(function (Post $post) {
             $post->raise(new Deleted($post));
+
+            Notification::whereSubject($post)->delete();
         });
 
         static::addGlobalScope(new RegisteredTypesScope);

src/User/User.php

@@ -125,6 +125,8 @@ class User extends AbstractModel
 
         static::deleted(function (User $user) {
             $user->raise(new Deleted($user));
+
+            Notification::whereSubject($user)->delete();
         });
 
         static::$dispatcher->dispatch(