Getting error while using GroupBy and Pagination in Eloquent - mysql

Question

I'm trying to use eloquent to get me a grouped by response and at the same time give me a Pagination response (The one that gives me the link to the second page).
I'm trying to do this:
App\Eating::Where('student_id', 2)->orderBy('created_at', 'DESC')->groupBy(function ($row) {
return Carbon\Carbon::parse($row->created_at)->format('Y-m-d');
})->paginate(25);
But, I'm getting this error when running it in the Tinker:
PHP warning: strtolower() expects parameter 1 to be string, object given in D:\Folder\vendor\laravel\framework\src\Illuminate\Database\Grammar.php on line 58
without the groupBy, I'm getting the correct result:
>>> App\Eating::Where('student_id', 2)->orderBy('created_at', 'DESC')->paginate(25)->toArray();
=> [
"total" => 1,
"per_page" => 25,
"current_page" => 1,
"last_page" => 1,
"next_page_url" => null,
"prev_page_url" => null,
"from" => 1,
"to" => 3,
"data" => [
[
"id" => 5,
"status" => "Comeu Bem",
"created_at" => "2017-07-05 13:55:25",
"updated_at" => "2017-07-05 13:55:25",
],
],
]
BUT, when I remove the pagination, I do get the error but only because I added the get():
>>> App\Eating::Where('student_id', 2)->orderBy('created_at', 'DESC')->groupBy(function ($row) {
... return Carbon\Carbon::parse($row->created_at)->format('Y-m-d');
... })->get();
PHP warning: strtolower() expects parameter 1 to be string, object given in D:\Joao\git\F1Softwares\Code\Server\F1Softwares\vendor\laravel\framework\src\Illuminate\Database\Grammar.php on line 58
>>>
>>>
>>> App\Eating::Where('student_id', 2)->orderBy('created_at', 'DESC')->groupBy(function ($row) {
... return Carbon\Carbon::parse($row->created_at)->format('Y-m-d');
... });
=> Illuminate\Database\Eloquent\Builder {#855}
Any idea what I could be doing wrong? I do need to have the orderBy AND the pagination, to make it easier for the app to show the results(It is a RestFul call).
Thanks,
João

Answer 1

You must call the groupBy() method on a collection, but it seems this won't work with paginate(). You could try using the forPage() method on the collection:
App\Eating::where('student_id', 2)->orderBy('created_at', 'DESC')
->get()->groupBy(function ($eating) {
return $eating->created_at->format('Y-m-d');
})->forPage(1, 25);
Also, just a note, you don't need to use Carbon to parse the date, Eloquent does this for you.
Alternatively, you could try to manually create your paginator once you have the collection grouped using Illuminate\Pagination\LengthAwarePaginator.
$eatings = App\Eating::where('student_id', 2)->orderBy('created_at', 'DESC')
->get()->groupBy(function ($eating) {
return $eating->created_at->format('Y-m-d');
});
$paginatedEatings = new LengthAwarePaginator($eatings, $eatings->count(), 25);
return $paginatedEatings->toArray();