A friend created a plugin for me which allows the users to mark posts as read or unread.
The code of this plugin is the following :

edit of the code !

<?php
/**
 * @package Read-Unread
 * @version 1.0
 */
/*
Plugin Name: Read-Unread
Plugin URI: http://www.google.fr
Description: Read-Unread plugin
Author: Moi
Version: 1.0
Author URI: http://www.google.fr
*/

global $wpdb;

$table_name = $wpdb->prefix . "users_read"; 

$sql = "CREATE TABLE IF NOT EXISTS `$table_name` (
  `ID_USER` int(11) NOT NULL,
  `ID_POST` int(11) NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=latin1;";

require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );

dbDelta( $sql );

function all_css()
{
    echo '
    <style>
        .post-read
        {
            cursor: pointer;
        }
    </style>';
}

function all_js()
{
    echo '
    <script>
        jQuery(function($)
        {
            $(".post-read").click(function()
            {
                action = $(this).data("action");

                if($(this).data("action") == "read")
                {
                    $(this).attr("src", "http://corentinbuet.fr/wordpress/wp-content/plugins/Read-Unread/LU.png");
                    $(this).attr("title", "Marquer comme Non lu");
                    $(this).data("action", "unread");
                }
                else
                {
                    $(this).attr("src", "http://corentinbuet.fr/wordpress/wp-content/plugins/Read-Unread/NON_LU.png");
                    $(this).attr("title", "Marquer comme Lu");
                    $(this).data("action", "read");
                }

                postID = $(this).data("id");

                var data = {
                    "action": action,
                    "idPost": postID
                };

                $.post("/wp-admin/admin-ajax.php", data, function(response)
                {

                });
            });
        });
    </script>';
}

function ajax_read() {
    global $wpdb;

    $idUser = intval(get_current_user_id());
    $idPost = intval($_POST['idPost']);

    $table = $wpdb->prefix . "users_read";
    $data = array('ID_USER' => $idUser, 'ID_POST' => $idPost);
    $format = array('%d','%d'); 

    $res = $wpdb->insert( $table, $data, $format );

    if($res == false)
    {
        return 1;
    }

    return 0;

    die();
}

function ajax_unread() {
    global $wpdb;

    $idUser = intval(get_current_user_id());
    $idPost = intval($_POST['idPost']);

    $table = $wpdb->prefix . "users_read";
    $where = array('ID_USER' => $idUser, 'ID_POST' => $idPost);
    $where_format = array('%d','%d'); 

    $res = $wpdb->delete( $table, $where, $where_format );

    if($res == false)
    {
        return 1;
    }

    return 0;

    die();
}

add_action( 'wp_ajax_read', 'ajax_read' );
add_action( 'wp_ajax_unread', 'ajax_unread' );

function get_img_read_unread()
{
    global $wpdb;

    $idUser = intval(get_current_user_id());
    $idPost = intval(get_the_ID());

    $msg = '';

    if($idUser > 0 &&  $idPost > 0)
    {
        $read = $wpdb->get_var( "SELECT COUNT(*) FROM wp_users_read WHERE ID_POST=$idPost AND ID_USER=$idUser");

        if($read == 1)
        {
            echo '<img class="post-read" data-action="unread" data-id="' . $idPost . '" src="https://corentinbuet.fr/wordpress/wp-content/plugins/Read-Unread/LU.png" title="Marquer comme Non lu">';
        }
        else
        {
            echo '<img class="post-read" data-action="read" data-id="' . $idPost . '" src="https://corentinbuet.fr/wordpress/wp-content/plugins/Read-Unread/NON_LU.png" title="Marquer comme Lu">';
        }
    }
}

function add_button($content)
{
    global $wpdb;

    $idUser = intval(get_current_user_id());
    $idPost = intval(get_the_ID());

    $msg = '';

    if($idUser > 0 &&  $idPost > 0)
    {
        $read = $wpdb->get_var( "SELECT COUNT(*) FROM wp_users_read WHERE ID_POST=$idPost AND ID_USER=$idUser");

        if($read == 1)
        {
            $msg = '<img class="post-read" data-action="unread" data-id="' . $idPost . '" src="https://corentinbuet.fr/wordpress/wp-content/plugins/Read-Unread/LU.png" title="Marquer comme Non lu">';
        }
        else
        {
            $msg = '<img class="post-read" data-action="read" data-id="' . $idPost . '" src="https://corentinbuet.fr/wordpress/wp-content/plugins/Read-Unread/NON_LU.png" title="Marquer comme Lu">';
        }
    }
$posttype = get_post_type( get_the_ID() );
if ($posttype == post)
{
    return $content . $msg;
}
else
{
    return $content;
}
}

add_filter('the_content', 'add_button');

add_action( 'wp_footer', 'all_js' );

add_action( 'wp_head', 'all_css' );


?>

I would like to mark as read a post when a post is opened by a user. So how could I do that ?

If i am not understandable enough, please let me know and i’ll try to explain better.

Thank you.

Corentin

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