Best way to query nested relationships in Laravel/Eloquent - mysql

Question

I have built an application with Laravel where I end up having rather deep-nested relationships, that I sometimes need to query. Database is MySQL.
For instance, I want to retrieve all Users who are allowed to read a Book. My data is structured as follows:
A User belongs to 0-n UserGroups through a UserMembership
A UserGroup has 0-n Rights
A Right relates to 1 Book and describes what action can be performed
After looking and browsing, I found that some people were recommending the following way to address nested relationships:
// class Book extends Model
public function readers() {
$bookId= $this->id;
return User::whereHas('memberships', function($m) use($bookId) {
$m->whereHas('group', function($g) use($bookId) {
$g->whereHas('rights', function($r) use($bookId) {
$r->where('resource_id', $bookId)->where('action', 'read');
});
});
});
}
I like that the code makes a lot of sense, but the performance is terrible.. Execution time is 430ms on average for Book::find(967)->readers()->get()
I re-wrote the function as follows:
public function readersNew() {
$bookId= $this->id;
$g = Right::where('resource_id', $bookId)->where('action', 'read')->pluck('group_id');
$uIds = UserMembership::whereIn('group_id', $g)->pluck('user_id');
return User::whereIn('id', $uIds);
}
With this code I achieve an average exec time of 4ms which is obviously much better. But this also looks much less "methodical" in terms of writing nested requests.
I would really like to understand :
why readers()->get() is so much slower than readersNew()->get()
what the best way is to write such requests

Answer 1

First of all, good job for improving the performance without even knowing why is it happening :)
Q1: why readers()->get() is so much slower than readersNew()->get()
Your readers()->get() function traverse in the hierarchy up to down which is why it makes more sense but its slower. It is same as running 3 foreach nested loops, it first returns all users which has membership and then iterate for each user and finds all the groups its belongs and then iterates each group and find the rights for each and then iterates each rights and gets the desired entry by matching resource_id and action.
whereas your readersNew()->get() traverse in the hierarchy down to up, that is why its faster. It first extracts the target group based upon the matched right and then extracts the membership, user associated with that group, hence faster.
Q2 what the best way is to write such requests
The approach readersNew()->get() is the best, you could just change your writing conventions to make more sense if you like:
public function readersNew() {
$bookId= $this->id;
$targetGroup = Right::where(['resource_id' => $bookId, 'action' => 'read'])->pluck('group_id');
$associatedUserIds = UserMembership::whereIn('group_id', $g)->pluck('user_id');
return User::whereIn('id', $associatedUserIds);
}
I hope it helps