setTotalCount example

$primary_data->setHasNextPage($has_next_page);

    // Calculate all the results and pass into a JSON:API Data object.     $count_query_cacheability = new CacheableMetadata();
    if ($resource_type->includeCount()) {
      $count_query = $this->getCollectionCountQuery($resource_type, $params, $count_query_cacheability);
      $total_results = $this->executeQueryInRenderContext(
        $count_query,
        $count_query_cacheability
      );

      $primary_data->setTotalCount($total_results);
    }

    $response = $this->respondWithCollection($primary_data, $this->getIncludes($request, $primary_data), $request, $resource_type, $params[OffsetPage::KEY_NAME]);

    $response->addCacheableDependency($query_cacheability);
    $response->addCacheableDependency($count_query_cacheability);
    $response->addCacheableDependency((new CacheableMetadata())
      ->addCacheContexts([
        'url.query_args:filter',
        'url.query_args:sort',
        'url.query_args:page',
      ]));