Use custom window-count based pager over pagerfanta

[veewee]

Q	A
Type	feature
BC Break	yes ❗
Fixed issues

Summary

Pagerfanta always executes double queries, just to count the amount of records:

• When the list query is rather heavy, this might slow down the application by a lot.
• In our code, we never do a second pagination within the same request, making this duplicate query execution obsolete.
• Counting is not always valid (left joins with aggregated group-by's can become quite hard)

Postgres already provides us with window partitions, making it possible to select the total count directly from the main query:
https://www.postgresql.org/docs/current/tutorial-window.html

This allows us to enhance the query like this:

SELECT 
    users.*,
   COUNT(1) OVER () AS total_results
FROM users
LIMIT 3 OFFSET 3

(which will work for any query: joined, aggregated, .... given it operates on the full query window)

Example implementation:

use Phpro\DbalTools\Pager\MappingPager;
use Phpro\DbalTools\Pager\Pager;
use Phpro\DbalTools\Pager\Pagination;
use Phpro\DbalTools\Pager\WindowCountPager;

$query = $connection->createQueryBuilder()->select('*')->from('users');
$userMapper = new UsersMapper()->convertFromDb(...);

$usersPager = new MappingPager(
    WindowCountPager::create(
        new Pagination(page: $page limit: $limit),
        $query,
    ),
    $userMapper,
);

This implementation makes it possible to run the same pagination queries on both dbal query builder and our custom composite queries.