How can I access a Discussion tag and content when building an extension?

JellyBool_1

Hi, I want to build a Flarum extension and I need some Discussion data when DiscussionWillBeSaved event fire.

My core code


 public function myListenMethod(DiscussionWillBeSaved $event)
    {
        $client = $this->getClient();
        $tag = $event->discussion->tags()->first(); // is this correct?
        $post = $event->discussion->posts()->first(); // is this correct?

        $client->createWork([
            'name'          => $event->discussion->title,
            'datePublished' => $event->discussion->start_time,
            'dateCreated'   => $event->discussion->start_time,
            'author'        => $event->discussion->actor->username,
            'tags'          => $tag->name, // Can I access a tag name here ?
            'content'       => $post->content, // Can I access a Discussion content here ?
        ]);
    }

Anyone can help?

Where can I find full docs about extension developing?

BTW，How to add a column to discussions table?