SQLSTATE[42000]: Syntax error or access violation: 1055 when using groupBy with hasManyThrough relation in Laravel - mysql

Question

When using groupBy on hasMany relation it is work fine but
when using groupBy on hasManythrough relation
in my controllr :
public function main()
{
# code...
$user = Auth::user();
$results = [
'vacations' => $user->vacations()->groupBy('type')->selectRaw('sum(days) as days,sum(mins) as mins, type')->get(), //works fine
'vactionRegisterd' => $user->vacationsRegisterd()->groupBy('type')->selectRaw('sum(days) as days,sum(mins) as mins, type')->get(), //works fine
'empVacations'=>$user->empVacations, //work fine
'employees_vacations'=>$user->empVacations()->groupBy('type')->selectRaw('sum(days) as days,sum(mins) as mins, type')->get(),//gives an error
];
return view('dashboard.dashboard', ['results' => $results]);
}
I have this error :
SQLSTATE[42000]: Syntax error or access violation: 1055
'hrweb.users.manager_id' isn't in GROUP BY (SQL: select sum(days) as
days,sum(mins) as mins, type, users.manager_id as
laravel_through_key from vacations inner join users on
users.id = vacations.user_num where users.manager_id = 5
group by type)I have tow tables users ,vacations
I don't know why (users.manager_id as laravel through key) is used even though I didn't use "users.manager_id" with "groupBy" or "selectRow" method.
My Code in user model :
1- user has many employees where employees are also users with different role and with manager_id != null [user->employees]
/**
* Get all of the employees from user table for the current admin User
*/
public function employees()
{
return $this->hasMany('App\Models\User', 'manager_id');
}
2- user has many vacations [user->vacations]
/**
* Get all of the vacations for the User
*/
public function vacations()
{
return $this->hasMany('App\Models\Vacations', 'user_num', 'id');
}
3- user hasManyThrough vacations [user->employees->vacation]
/**
* Get all of the employees vacations for the User
*/
public function empVacations()
{
return $this->hasManyThrough(Vacations::class, User::class, 'manager_id', 'user_num', 'id', 'id');
}

Answer 1

By reading the Error again ,I noted that Laravel use the foreign key as laravel_through_key in the query in some way.
The problem solved by adding laravel_through_key in the groupBy() method like this :
[...
'employees_vacations'=>$user->empVacations()
-> groupBy('laravel_through_key','user_num','type')
-> selectRaw('sum(days) as days,sum(mins) as mins,user_num, type')->get()
]
But I still think there is a better solution so I will be happy to know your answers ^_^