Count how many users are there per each category - php

Question

I'm trying to get user data, them get department value to array so I can group it and count how many users are part of the same department.
User table:
Schema::create('users', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->string('email')->unique();
$table->timestamp('email_verified_at')->nullable();
$table->string('password');
$table->rememberToken();
$table->timestamps();
});
Department table:
Schema::create('departments', function (Blueprint $table) {
$table->increments('id');
$table->timestamps();
$table->string('name');
});
Assignment table:
Schema::create('assignments', function (Blueprint $table) {
$table->increments('id');
$table->timestamps();
$table->string('name');
$table->unsignedInteger('user_id')->nullable();
$table->foreign('user_id')->references('id')->on('users');
$table->unsignedInteger('department_id')->nullable();
$table->foreign('department_id')->references('id')->on('departments');
});
public function setDepartment($users)
{
$departmentArray = [];
$users = DB::table('users')
->leftJoin('assignments','assignments.user_id','=','users.id')
->leftJoin('departments','assignments.department_id','=','department.id')
->select('assignments.id as assignments',
'assignments.name as assignment_name',
'departments.id as dept_id',
'departments.name as dept_name',
'users.id as user_id',
'users.name as user_name'
)
->where('user_id','=',$users->id)
->get();
foreach($users as $user) {
$assignments = $user->assignments;
$dept_id = $user->dept_id;
$departmentArray[$user->dept_id] = $user->dept_name;
}
$users->department = $departmentArray;
$users->dept_id = $dept_id;
}
}
Then whenever I try to call this like:
public function index() {
$users = DB::table('users')->get();
$users = $this->setDepartment($users);
return view('/users/list', [
'users' => $users
]);
}
I receive
"Trying to get property 'user_id' of non-object"

Answer 1

'A department has many users through assignments'
Documentation for hasManyThrough: https://laravel.com/docs/5.7/eloquent-relationships#has-many-through
Departments Model:
public function users()
{
return $this->hasManyThrough('App\User', 'App\Assignment');
}
'Count how many users there are for each department'
Departments controller:
public function index()
{
$departments = Department::all();
foreach($departments as $department)
{
// This line returns the number of users for the department
// Use this however you please
$department->users->count();
}
}
Documentation for count() found here: https://laravel.com/docs/5.7/eloquent#retrieving-aggregates
You can work out the reverse of the relationship if you need to go from users to department, but I would suggest looking into eloquent, it can be quite handy for queries such as these. Let me know if you need any further clarification.
Edit:
For access from user to department, this is one way of defining the relationships.
User Model:
// A user belongs to many departments through their assignments
public function departments()
{
return $this->hasManyThrough('App\Department', 'App\Assignment');
}
This way you can access the departments of the user like so:
$departments = $user->departments();
And iterate through the $departments, accessing the count() as explained above.