README

Why make the package:

When using AbstractCursorPaginator::through() or AbstractCursorPaginator::getCollection()->transform() to transform each item, and serializing (e.g. toArray(), toJson()) implicitly or obviously will give an error: Undefined index, Paginate and SimplePaginate don't have this problem.

This error occurs in AbstractCursorPaginator::getParametersForItem():

https://github.com/laravel/framework/blob/bdc707f8b9bcad289b24cd182d98ec7480ac4491/src/Illuminate/Pagination/AbstractCursorPaginator.php#L218

When pagination has previous page or next page, the method will be called. The error occurs because AbstractCursorPaginator need a field to get the page cursor. For example, we have a user model, it contain 'id' and 'name' field. We call User::cursorPaginate(n) to get a CursorPaginator instance, when the paginator serialized, AbstractCursorPaginator::getParametersForItem() be called. Please see source link above, $item is a user model instance like { id: 1, name: 'someone', ...}, $parameterName in callback block is "user.id", the result is 'id':

$item[$parameterName] ?? $item[Str::afterLast($parameterName, '.')]
// $item doesn't have key named 'user.id', so run next, get the user's id

If transforming paginate items, because cannot access exist key, we will give an error: Undefined index: id,

// $item: {extra_field: '...', origin: [user instance]}
$item[$parameterName] ?? $item[Str::afterLast($parameterName, '.')]
// $item doesn't have key named 'user.id', so run next, but $item doesn't have key named 'id' either. give an error: `Undefined index: id`

How the package fix it:

Overriding Illuminate\Pagination\AbstractCursorPaginator::through() to register a callback for mapping each item in the slice of items to the "data" field when serialized. It's works because it not changed origin $items, it can avoid Undefined index error.

How to use:

Just use through() method as before.