Eager load for collections on the fly - laravel

Question

I have this, user has many to many property via pivot property_users.
I am making somehow reusable classes in my webapp.
These are the models with their eager loading functions:
//User model
public function properties()
{
return $this->belongsToMany(Property::class, 'property_users', 'user_id', 'property_id');
}
//Property model
public function property_users()
{
return $this->hasMany(PropertyUser::class, 'property_id', 'id');
}
//PropertyUser model
public function user()
{
return $this->belongsTo(User::class);
}
//GetProperties class
public function handle()
{
return auth()->user()->properties()->get();
}
//somewhere in a feature
$properties = $this->run(GetProperties::class);
//this returns valid properties under the logged in user
I now need to get the chat_username in property_users that belongs to this user
I manage to make it work if I loop through the properties and then doing it on the fly.
$properties = $properties->map(function($property) {
$propertyUsers = $property->property_users()->get();
$chatUsername = null;
foreach($propertyUsers as $propertyUser) {
if($propertyUser->property_id == $property->id) {
$chatUsername = $propertyUser->chat_username;
}
}
return [
'name' => $property->name,
'id' => $property->id,
'chat_username' => $chatUsername
];
});
But I am trying to reduce query on loop to reduce hits especially when they are on multiple properties in the database.
The other way is that I can add the property_users in the eager loading under GetProperties class by updating it to:
$query = Property::query();
$query->with(['property_users']);
$query->whereHas('property_users', function($qry) {
$qry->where('user_id', Auth::user()->id);
});
$properties = $query->get();
return $properties;
But I do not want to rely on adding more eager loading to the original GetProperties class as the GetProperties will get fat and I do not really need those data (let's say adding property_invoices, property_schedules, etc but not really needing it in some area).
Rather, I want to do the eager loading on the fly but with a twist! This is how I would imagine it:
Collect all the ids from the properties, do the fetch using wherein and apply all the users to the properties in a single query. This way it will be even more beautiful.
Maybe something like this: (using the original GetProperties class)
$properties = $this->run(GetProperties::class);
//this does not work. The error is: Method Illuminate\Database\Eloquent\Collection::property_users does not exist.
$property->property_users = $properties->property_users()->get();
Would be great if someone can show me how to do it.

Answer 1

What about eager loading only the fields you actually need?
$query->with('property_users:id,user_id');
The model will not get fat, and you will not need to do separate queries in the loop.
It is documented in the official documentation: https://laravel.com/docs/5.8/eloquent-relationships#eager-loading , see Eager Loading Specific Columns
Edit: if you want to perform the query after the GetProperties class, you will need to collect all the ids and perform a second query. I honestly don't like this second approach, because it is far slower, less performant and I consider it less elegant then adding a single line in the GetProperties class, but it is gonna work:
$properties = $this->run(GetProperties::class);
$ids = $properties->pluck('id'); // Get all the ids as an array
$propertyUsers = propertyUsers::whereIn('property_id', $ids)->get(); // Get the propertyUsers model
foreach($properties as $property) {
$property->property_users = $propertyUsers->where('property_id', $property->id); // Not even sure you can do that, proerty_users may not been writable
}

Answer 2

Alright, after reading here and there.
I found this article: https://laravel-news.com/eloquent-eager-loading
The solution is really nice. Simply:
$properties = $this->run(GetProperties::class);
//lazy load
$properties->load('property_users');
$properties = $properties->map(function($property) {
$user = $property->property_users->first(function($user) {
if($user->user_id == Auth::user()->id) {
return $user;
}
})->only('chat_username');
return [
'name' => $property->name,
'id' => $property->id,
'chat_username' => $user['chat_username']
];
});
After checking query logs:
//auth query done by middleware
[2019-05-21 07:59:11] local.INFO: select * from `users` where `auth_token` = ? or `temporary_auth_token` = ? limit 1 ["token_removed_for_security_purpose","token_removed_for_security_purpose"]
//These are the queries made:
[2019-05-21 07:59:11] local.INFO: select `properties`.*, `property_users`.`user_id` as `pivot_user_id`, `property_users`.`property_id` as `pivot_property_id` from `properties` inner join `property_users` on `properties`.`id` = `property_users`.`property_id` where `property_users`.`user_id` = ? [8]
[2019-05-21 07:59:11] local.INFO: select * from `property_users` where `property_users`.`property_id` in (2, 4)
This way, I can keep my GetProperties as small as possible, then just lazy load it whereever I need it.