Querying counts from large datasets using eloquent - laravel

Question

I have the following relationships:
A Job has many Roles.
public function roles()
{
return $this->hasMany(Role::class);
}
A Role has many Shifts and Assignments through shifts.
public function shifts()
{
return $this->hasMany(Shift::class);
}
public function assignments()
{
return $this->hasManyThrough(Assignment::class, Shift::class);
}
A Shift has many Assignments.
public function assignments()
{
return $this->hasMany(Assignment::class);
}
I need to get a count of all assignments with a certain status, let's say "Approved". These counts are causing my application to go extremely slowly. Here is how I have been doing it:
foreach ($job->roles as $role){
foreach ($role->shifts as $shift) {
$pendingCount = $shift->assignments()->whereStatus("Pending")->count();
$bookedCount = $shift->assignments()->whereIn('status', ["Booked"])->count();
}
}
I am certain that there must be a better, faster way. Some of these queries are taking upwards of 30+ seconds. There are hundreds of thousands of Assignments, which I know is affecting performance. How can I speed up these queries?

Answer 1

You're running into the N+1 issue here a few times. You want to lazy load the nested assignment through jobs then you can access the relation and your where() and whereIn() calls are executed on the returned collection instead of on the query builder which is why you have to use where('status', "Pending") instead of whereStatus("Pending") in my example because the collection won't automatically resolve this constraint:
$job = Job::with('roles.assignments')->find($jobId);
foreach ($job->roles as $role) {
$pendingCount = $role->assignments->where('status', "Pending")->count();
$bookedCount = $role->assignments->whereIn('status', ["Booked"])->count();
}
This should be a lot quicker for you.
UPDATE
You could even take that one step further and map the result and store the results in a property on the role:
$job->roles->map(function($role) {
$role->pending_count = $role->assignemnts->where('status', "Pending")->count();
$role->booked_count = $role->assignments->whereIn('status', ["Booked"])->count();
return $role;
});