Filtering.Custom Filter (Simple Version)

        protected function doGetCustomTemplate($type, $part, $mode, &$result, &$params)
        {
            if ($part == PagePart::GridToolbar && $mode == PageMode::ViewAll) {
                $result = 'custom_simple_filter_grid_toolbar.tpl';
            
                $lifeExpectancyFilter = array(
                    'min' => 35,
                    'max' => 90
                );
                if (isset($_SESSION['simpleLifeExpectancyFilter'])) {
                    $lifeExpectancyFilter = array_merge($lifeExpectancyFilter, $_SESSION['simpleLifeExpectancyFilter']);     
                } 
                
                $params['LifeExpectancyFilter'] = $lifeExpectancyFilter; 
            }
        }

        protected function DoPrepare() {
            // handling custom filter parameters
            $lifeExpectancyFilter = array(
                'min' => -1,
                'max' => -1
            );
               
            if (GetApplication()->isGetValueSet('simpleLifeExpectancyFilter')) {
                $lifeExpectancyFilterValue = GetApplication()->GetGETValue('simpleLifeExpectancyFilter');
                if (is_array($lifeExpectancyFilterValue)) {
                    $lifeExpectancyFilter = array_merge($lifeExpectancyFilter, $lifeExpectancyFilterValue);
                }
            } elseif (isset($_SESSION['simpleLifeExpectancyFilter'])) {
                $lifeExpectancyFilter = array_merge($lifeExpectancyFilter, $_SESSION['simpleLifeExpectancyFilter']);
            }
            
            if ($lifeExpectancyFilter['min'] !== -1 && $lifeExpectancyFilter['max'] !== -1) {
                $this->dataset->AddCustomCondition(
                    sprintf('life_expectancy >= %d AND life_expectancy <= %d', 
                        $lifeExpectancyFilter['min'], $lifeExpectancyFilter['max']
                    )    
                );
                $_SESSION['simpleLifeExpectancyFilter'] = $lifeExpectancyFilter;
            } else {
                unset($_SESSION['simpleLifeExpectancyFilter']);
            }
            
            // auxiliary code
            $this->setDescription(file_get_contents("external_data/doc/filtering_custom_filter_simple.html"));
            
            $this->setDetailedDescription(
                '<br>' .
                '<div id="on-get-custom-template" class="event-code">' .
                    extractMethodCode($this, 'doGetCustomTemplate') . '</div>' .
                '<div id="on-prepare-page" class="event-code">' .
                    extractMethodCode($this, 'doPrepare') . '</div>' .
                '<div id="custom-grid-toolbar" style="display: none;">' .
                    extractTemplateFileCode('components/templates/custom_templates/custom_simple_filter_grid_toolbar.tpl') . 
                '</div>' .
                '<div id="custom-simple-filter" style="display: none;">' .
                    extractTemplateFileCode('components/templates/custom_templates/custom_simple_filter.tpl') . 
                '</div>'
            );
        }