how to make a subquery using the query builder of laravel - sql

Question

I want to do the following mysql query with the query builder of Laravel 7:
SELECT r.id, (SELECT date FROM posts as pp where r.id = pp.request_id
ORDER BY STR_TO_DATE(SUBSTRING(pp.date, 1, 19),'%Y-%m-%dT%H:%i:%s') DESC limit 1), r.delivery_mode FROM requests AS r
LEFT JOIN posts AS p ON r.id = p.request_id
group by r.id;
However unfortunately I don't understand how to obtain the latests post date for every request using the query builder of Laravel. I suppose I should do a subquery as in the query above. This is my code:
$query = DB::table('requests');
$query->select(DB::raw('DISTINCT(requests.id)'),'requests.delivery_mode',DB::raw('posts.date'));
$query->leftJoin('posts', 'requests.id', '=', 'posts.request_id');
$requests_list = $query->get();
In the table posts, the date is a string in this format: 2020-04-16T12:46:33+02:00. So I used that complicated functions because I want to see only the latest date post grouped by id_request, that is the foreign key of the table posts connected with the primary key id of the table requests. A request can have many posts.
Can help?
PS:
I found the solution:
$query = DB::table('requests');
$query->select(DB::raw('DISTINCT(requests.id)'),'requests.delivery_mode',DB::raw("(SELECT date FROM posts as pp where requests.id = pp.request_id ORDER BY STR_TO_DATE(SUBSTRING(pp.date, 1, 19),'%Y-%m-%dT%H:%i:%s') DESC limit 1) as lastPostDate"));
$query->leftJoin('posts', 'requests.id', '=', 'posts.request_id');
$requests_list = $query->get();
Probably it isn't a pretty solution but it works!.

Answer 1

Request Model
public function posts()
{
return $this->hasMany(Post::class);
}
Post Model
public function request()
{
return $this->belongsTo(Request::class);
}
Controller
public function index()
{
$date = Post::has("request")
->orderBy(...) // add your order by condition here
->limit(1)
->pluck("date");
$requests = Request::with("posts")
->where("date", $date)
->get();
return $requests;
}