Option to add row count lazily

[MieskeB]

Hi everyone! For our project, we have a huge table displayed using datatables-bundle. Because of the forced 'count' queries, the request becomes extremely slow. Therefore, I have implemented the option to lazily count the amount of rows displayed.

Current flow in ORMAdapter.php:

1. Build query
2. Count ALL results
3. Apply filters
4. Count filtered results
5. Fetch 50 rows
6. Return everything

Mostly step 2, but also step 4 make the request much longer when big tables are being used. Therefore, I added an option to use the following flow (default remains the top flow).

1. Build query
2. Fetch 50 rows
3. Return rows immediately
4. Count results later in a separate request

To the ORMAdapter, the following properties can be added:

Property	Type	Default	Description
lazy_total_count	bool	false	adds lazy loading to the total count
lazy_filtered_count	bool	false	adds lazy loading to the filtered count

This is controller code is used in my test project:

    #[Route('/', name: 'app_index')]
    public function index(Request $request, DataTableFactory $factory): Response
    {
        $table = $factory->create()
            ->add('email', TextColumn::class, ['field' => 'u.email'])
            ->add('iban', TextColumn::class, ['field' => 'u.iban'])
            ->add('name', TextColumn::class, ['field' => 'u.name'])
            ->createAdapter(ORMAdapter::class, [
                'entity' => User::class,
                'query' => function (QueryBuilder $qb) {
                    $qb->select('u')->from(User::class, 'u');
                },
                'lazy_total_count' => true,        // <-- This line adds lazy counting to the total count
                'lazy_filtered_count' => true,     // <-- This line adds lazy counting to the filtered count
            ]);

        $table->handleRequest($request);

        if ($table->isCallback()) {
            return $table->getResponse();
        }

        return $this->render('index/index.html.twig', ['datatable' => $table]);
    }

Tests and documentation have also been included

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.21%. Comparing base (f29e574) to head (f07c810).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #410   +/-   ##
=======================================
  Coverage   95.21%   95.21%           
=======================================
  Files          40       40           
  Lines        1087     1087           
=======================================
  Hits         1035     1035           
  Misses         52       52           

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