How to get URL param for pagination in shortcode?

Question

I have made the shortcode which displays data from database. There are so many rows and so I made pagination. But I can't get the URL param which means page number.

<?php

/**
 * Plugin Name: Plugin hell
 */

if (!defined('ABSPATH')) {
    die;
}

function count_rows()
{
    global $wpdb;
    $table_name = $wpdb->prefix . 'strong_concordance';
    $count = $wpdb->get_var("SELECT COUNT(*) FROM $table_name");
    return intval($count);
}
function get_data($offset, $per_page)
{
    global $wpdb;
    $table_name = $wpdb->prefix . 'strong_concordance';
    $data = $wpdb->get_results("SELECT * FROM $table_name LIMIT $offset, $per_page");
    return $data;
}


function display_data_shortcode($atts)
{
    $atts = shortcode_atts(
        array(
            'page' => 1,
            'per_page' => 10,
        ), $atts, 'display_data');

    //$page = intval($atts['page']);
    $page = (get_query_var('page')) ? get_query_var('page') : 1;
    var_dump($page);

    $per_page = intval($atts['per_page']) ? : 10;

    $num_pages = ceil(count_rows() / $per_page);

    $offset = ($page - 1) * $per_page;

    $data = get_data($offset, $per_page);
    
    $output = '';
    foreach ($data as $row) {
        $output .= '<h3>' . $row->strong_reference . '</h3>';
        $output .= '<p style="font-weight: bold;">' . $row->greek_word . '</p>';
        $output .= '<p>' . $row->explanation . '</p>';
    }
    

    if ($page > 1) {
        $output .= '<a href="?page=' . ($page - 1) . '">Previous</a>';
    }
    for ($i = 1; $i <= $num_pages; $i++) {
        $output .= '<a href="?page=' . $i . '">' . ' ' . $i . ' ' . '</a>';
    }
    if ($page < $num_pages) {
        $output .= '<a href="?page=' . ($page + 1) . '">Next</a>';
    }

    return $output;
}

add_shortcode('display_data', 'display_data_shortcode');

?>

There will be page numbers like "1 2 3 4 5 ... ". I click any number-for example 4, the $page should be 4 and so $offset should be 30, but the $page is still 1 and so there will be same data. How can I solve this issue?

Answer 1

You can use get_query_var('paged'), this will return the current page in pagination.

$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;

Or the shorter form

$paged = get_query_var('paged') ?: 1;