Laravel: Use order by in combination with whereHas - laravel

Question

I want to retrieve a collection of data, which is ordered by the start_date of the relation
Basically I want to achieve this, with Laravel Models (the code below works perfectly)
$posts = DB::table('posts')
->leftJoin(
'threads',
'posts.id',
'=',
'threads.postable_id'
)
->where('threads.postable_type', '=', 'App\Post')
->orderBy('threads.start_date')
->paginate($request->input('limit', 2));
So in this case, I'm fetching ALL Posts and those are ordered by the start_date of the thread relation.
Those are not my actual tables but this works perfectly!
Because I'm using https://laravel.com/docs/8.x/eloquent-resources this is not the ideal solution to retrieve sorted data.
So instead I want to use the orderBy clause somewhere here
$posts = Post::whereHas('thread', function ($query) {
$query->where('end_date', '>=', Carbon::now());
});
But I just cannot make this work. I've tried this
$posts = Post::whereHas('thread', function ($query) {
$query->where('end_date', '>=', Carbon::now())
->orderBy('start_date');
});
and I also appended this to the actual relation:
public function thread(): MorphOne
{
return $this->morphOne('App\Thread', 'postable')->orderBy('start_date');
}

Answer 1

If you look at your code:
$posts = Post::whereHas('thread', function ($query) {
$query->where('end_date', '>=', Carbon::now())
->orderBy('start_date');
});
the whereHas will only return Post associate with a thread which the function return true.
Try this:
$posts = Post::with('thread')->has('thread')->orderBy('thread.start_date')->get();
This will fetch all Post with Thread only if they have at least one Thread and then orderBy the start_date of the Thread.
You don't have to do the whereHas function because when you call ->with('thread') it'll use you this :
public function thread(): MorphOne
{
return $this->morphOne('App\Thread', 'postable')->orderBy('start_date');
}
whereHas doesnt retrieve the relationship.
If you need even more power, you may use the whereHas and orWhereHas methods to define additional query constraints on your has queries, such as inspecting the content of a comment: Laravel whereHas
Don't do :
$posts = Post::with('thread')->orderBy('thread.start_date');
If there is no thread on some post, post without thread will be fetch with value null for their key thread and you will have an unexpected result when you try to orderBy.

Answer 2

First of all I want to thank Elie Morin for his help but I found out that I definitely need to use joins for that task.
In my example, I wanted to order the main query (posts) by the relation's start_date
Doing what you suggested
$posts = Post::with('thread')->has('thread')->orderBy('thread.start_date')->get();
Would only order the thread by start_date and not the ENTIRE query.
Which is why I came up with something like this:
$posts = Post::has('thread')
->select('posts.id')
->leftJoin(
'thread',
'posts.id',
'=',
'thread.postable_id'
)
->where('thread.postable_type', '=', 'App\Post')
->where('thread.end_date', '>=', Carbon::now())
->orderBy('thread.start_date')
->with('thread');
return PostResource::collection($posts->paginate(2));