Get all objects that exist in two collections - laravel

Question

I'm building a Laravel page on which I want to show a list of lessons. Which lessons should be on the page is filtered by three criteria (of which all should be true):
The lesson is active, ie "where('active', true)". Simple enough.
The lesson is part of a track that the user has chosen. Models are set up with belongsToMany() (it is a many-to-many relationship), so I can get these lessons by a simple $track->lessons.
This is where it gets tricky. Some lessons should only be visible to users with certain titles (ie there is a many to many between titles and lessons). I can get the lessons with the correct title requirement using Auth::user()->title->lessons.
Question is how I get all this together. The best I've come up with this far is the following:
$title = Auth::user()->title;
$lessons = Lesson::where('active', true)
->whereIn('id', $track->lessons->pluck('id'))
->where(function ($query) use($title) {
$query->whereIn('id', $title->lessons->pluck('id'))->orWhere('limited_by_title', false);
})
->get();
...which is crap ugly, clearly suboptimal and (for some reason I really don't understand) also won't work (I don't get the lessons my title entitles me to in my list). Been struggling for quite some hours now, I get the feeling that I'm overcomplicating, first plucking id's and then using them in a whereIn() can't possibly be a good way of doing this.
So I can easily enough get a collection of lessons in the track, and I can get a collection of lessons belonging to the title, but how do I get all objects that exist in both those collections?

Answer 1

Using whereHas() is the answer to your concerns about plucking IDs. Instead of running additional queries to retrieve IDs, whereHas() will attach the constraint to the original query as a subquery on the related tables.
Breaking the query down to its parts:
1: Answered
2: Assuming the inverse of $track->lessons is $lesson->tracks, and $track is coming from code you didn't include:
$lessons = Lesson::whereHas('tracks', function ($query) use ($track) {
$query->where('id', $track->id);
})
3: Assuming the inverse of $title->lessons is $lesson->titles:
$lessons = Lesson::where(function ($query) use ($title) {
$query->whereHas('titles', function ($query) use ($title) {
$query->where('id', $title->id);
})
->orWhere('limited_by_title', false);
})
Combined back into one:
$track = ???;
$title = Auth::user()->title;
$lessons = Lesson::where('active', true)
->whereHas('tracks', function ($query) use ($track) {
$query->where('id', $track->id);
})
->where(function ($query) use ($title) {
$query->whereHas('titles', function ($query) use ($title) {
$query->where('id', $title->id);
})
->orWhere('limited_by_title', false);
})
->get();
If this still doesn't give the results you were expecting, you can examine the full query being run by replacing get() with toSql(). Sometimes working from the ORM as a starting point instead of the SQL can lead you down the wrong path. For even more detail to debug and understand the queries being run, you can enable query logging: https://laravel.com/docs/5.7/database#listening-for-query-events

Answer 2

intead of where use whereHas on "titles" relationship
$title = Auth::user()->title;
$lessons = Lesson::where('active', true)
->whereIn('id', $track->lessons->pluck('id'))
->whereHas('titles',function ($query) use($title) {
$query->whereIn('id', $title->pluck('id'))
->orWhere('limited_by_title', false);
})->get();

Answer 3

First of all complicated, really complicated. Your table structure needs serious modification to make it easier.
However, considering you don't want to go down that road, you could do it simpler by using join
Assuming you have following table structure:
users
titles (has user_id foreign key)
lessons (has title_id foreign key)
tracks (has lesson_id foreign key)
$trackName = $request->input('track_name');
$title = Auth::user()->title;
$lessons = Lesson::join('tracks', 'lessons.id', '=', 'tracks.lesson_id')
->join('titles', 'lessons.title_id', '=', 'titles.id')
->where('lessons.active', true)
->where('tracks.track_name', $trackName)
->where(function ($query) use($title) {
$query->where('titles.id', $title->id)->orWhere('lessons.limited_by_title', false);
});
dd($lessons);
That is of course if your users table and titles have one to one relationship otherwise pluck all title_ids and use whereIn instead of where for titles.id query.
I hope you have enough understanding of laravel framework to understand and implement this solution.
Sorry, I don't have enough time to proofread or give more details.
Good luck!
Good luck if you need pagination after that :p I doubt simple ->paginate() will work :D
I hope it helps