Optimising query (loop inside loop)

Yes, eager-load the topics associated with the category(ies), you can do this all in a single Eloquent statement assuming the appropriate relationships are present and correct:

$subject = Subject::with('categories.topics')->find($subjectId);

Now, the Subject instance will have a categories property which is a Collection of Category instances; and further, each Category instance will have a topics property which is a Collection of the associated Topic instances. This will result in exactly 3 queries, one for Subject one for all of the Categories, and one for all of the Topics - Laravel will put together the Category instances with their associated Topics.

In your view:

@foreach($subject->categories as $category)
	{{ $category->name }}
	@foreach($category->topics as $topic)
		{{ $topic->name }}
	@endforeach

@endforeach

I get that, however I'm not sure how would I display all of them inside a loop. I want to show all categories, and under each one all topics.

under each one all topics

Do you mean every topic - not just the topics associated with the current Category? You could make one extra query for all Topics:

$topics = Topic::all();

Then what; you want to display every topic under each displayed Category, and highlight the associated ones? You can check the current Category's topics Collection includes the current topic (from the all topics Collection):

@foreach ($categories as $category)

	@foreach ($topics as $topic)

		{{ $topic->name}} 
		
        @if ($category->topics->includes($topic)) 
			// display a check mark or whatever
		@endif	
		
	@endforeach

@endforeach

I mean to show the appropriate ones - with eager load I'm grabing subject with categories and topics. But in my view do I still have collections $categories and $topics even though I'm not using it in my controller?

No, if you were to use the following:

$subject = Subject::with('categories.topics')->find($subjectId);

then everything you need is inside the $subject object, i.e. $subject->categories, and each $category has $category->topics - like I described earlier.

OK, I'try that. Thnx

All worked fine - I was down to 3 queries - until I've added a tag to count lessons under each category and topic.

I tried using withCount but it doesn't calculate individual categories, only overall number of lessons belonging to subject.

If i do count like this $category->lessons->count() the number of queries jump to 45!