Using date_parse_from_format on PHP 5.2

Last week, I was working on a problem of the Datepicker formats been really weird on some cases for The Events Calendar plugin, as Modern Tribe does support WordPress minimum PHP required version for it's plugins, the developers have to solve some problems with the Tools that PHP 5.2 provides us.

The enemy! ?

Fatal error: Call to undefined function date_parse_from_format()

On the case of dates, this becomes a real problem since we don't have support for the date_parse_from_format or DateTime::createFromFormat() we needed to be able to parse formats like 15/02/1993 formatted with d/m/Y.

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Is.JS a general purpose check library

Working on a way to consistently check for values when dealing with JavaScript conditionals, and as you might already know from one or two articles written previously by some experienced developers out there.

To solve my issue I found a very cool library that will deal with almost all the basic conditionals in a pretty readable way, it's called is.js. Check out the library's GitHub repository and follow the project to know more about it.

What sold it for me was the tiny file size, no dependencies what so ever and a very good performance, that's why it's called a "micro" library.

Modify Category Queries in WordPress

WordPress has a lot of powerful tools that will speed up the development process by a great amount, the first one that you will encounter when creating themes is the WP_Query.

For those who are not aware of what is the WP_Query, you can assume its the WordPress tool that will give you control over the Queries made to fetch posts in the database.

On this article I will talk a little bit of how to change and modify your WordPress theme or plugin to allow better control over the WP_Query taxonomies Module, which gives the developer a very easy way to handle the Taxonomy related searches within WordPress. Read More

Get Attachment ID by image URL

This week I was doing some a development review for a Agency here in Rio and we saw that we needed to discover the Attachment ID based on the URL.

On version 4.0 WordPress introduced a function to allow you to grab the Attachment ID by image URL. Read More

How to use WordPress icon on a Plugin

When you are using the WordPress structure to build your plugin from time to time you will need to insert an icon to make your plugin easier on the eye.

A little while ago a few developers and designers found out that using images to display simple Icons was a bad idea, because of the way it scales in to Mobile and the lack of methods to change it's color. These guys found out that the best way was to use .svg files, which are a vector with the drawing instead of a bitmap. Read More

How deprecate code on WordPress Plugin

As you start to develop plugins to sell or distribute for free on the WordPress plugin repository you will see yourself in one of the worst situations as a product developer.

In order to improve your code you will need to let go of old code and introduce new stuff to the codebase.

You will face the following problem, how will you do it without breaking themes and other plugins that rely on your current code?

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Using a Meta value on Post Title

I saw a tweet earlier today of a user asking how to solve common issue, how to use a single variable inside of the title of my WordPress posts, in this case events.

How to do it

To understand how to do this task you first need to see that these kind of variables can be used inside of title without been inserted manually on by applying a little concept called filter, which will allow you to hook to a WordPress method and apply X or Y function to solve your issue. Read More

How to use AJAX on WordPress

If you already know what is an AJAX request please just jump right to the section where I will talk about how to start coding.

What is an AJAX request

First you will need to understand that an AJAX request is nothing more then a simple GET or POST to an URL that you defined, you will pass some parameters and this URL should answer you with some other data that you will be able to parse on the JavaScript and using it you will be able to give your users the needed visual feedback.

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Display online Users on WordPress

Earlier today I ran into a problem where I needed a simple way to display which registered users are online right now on the site.

I've done a Video explaining what was my solution and how to apply it to a theme, but I myself hate when I see a video without any code that I can easily take a look at, so below the video you will find a explanation of the code step by step, and in the end the plugin I created for this purpose.

Please note that I will comment further the code on the video, but there are some comments on each one of the snippets here

Variables used

We will use only two variables on this plugin:

  • static protected $_instance = null; -- Holds the static instance of our class after the plugin is initialized
  • static protected $prefix = 'OnlineNow'; -- Prefix we will use on the Database Options

Class Instance handling

When dealing with plugins in WordPress a good practice is to save a static variable of the main class on a private/protected variable and create a static method to instantiate the class whenever you call this method the first time:

static public function instance(){
    null === self::$_instance and self::$_instance = new self;
    return self::$_instance;

Plugin Initialization

Here is where our plugin will hook into WordPress and do the required actions to allot this plugin to work as we expect.

static public function init(){
    // Lock this class to be initialized only once
    if ( null !== self::$_instance ){
        return false;
    add_action( 'wp_login', array( self::instance(), 'login' ), 10, 2 );
    add_action( 'clear_auth_cookie', array( self::instance(), 'logout' ), 10 );

    // Register Shortcodes
    add_shortcode( 'online:list', array( self::instance(), 'shortcode_list' ) );
    add_shortcode( 'online:qty', array( self::instance(), 'shortcode_qty' ) );

    add_filter('widget_text', 'do_shortcode');

    return true;

Register when a User logs in

We need to register when a user do the login so that we can save it in the database to grab this value and display for the users.

public function login( $user_login, $user ) {
    $users = get_option( self::$prefix . '-users', array() );

    if ( in_array( $user->ID, $users ) ){

    $users[] = $user->ID;

    update_option( self::$prefix . '-users', $users );

Register when a User logs out

Just like when we register the action of login and add the user ID to the database option, now we will remove that ID when the user logs out.

public function logout() {
    $users = get_option( self::$prefix . '-users', array() );

    $user_id = get_current_user_id();

    if ( ! in_array( $user_id, $users ) ){

    update_option( self::$prefix . '-users', array_diff( $users , array( $user_id ) ) );

Grab the users logged in

We need a method that will allow us to get the users from the database option, I've also allowed the developer to exclude or include a user to the list.

public function get_users( $include = array(), $exclude = array() ){
    // Retrieve the users from Database
    $users = get_option( self::$prefix . '-users', array() );

    // Parse Shortcode atts to exclude
    if ( is_string( $exclude ) ){
        $exclude = array_map( 'trim', explode( ',', $exclude ) );

    // Exclude users based on shortcode attribute
    $users = array_diff( (array) $users, (array) $exclude );

    // Parse Shortcode atts to include
    if ( is_string( $include ) ){
        $include = array_map( 'trim', explode( ',', $include ) );

    // Include users based on shortcode attribute
    $users = array_merge( (array) $users, (array) $include );

    // Garantee that the array is safe for usage
    $users = array_unique( array_filter( (array) $users ) );

    // Remove all non existent users
    $users = array_map( array( $this, 'user_exists' ), $users );

    // Garantee that the array is safe for usage
    $users = array_filter( (array) $users );

    return $users;

Then I used a method inside of the get_users to check if the user exists before return the list of WP_User objects - on video.

public function user_exists( $user_id ){
    $user = new WP_User( $user_id );

    // Check if the users exists
    if ( ! $user->exists() ){
        return false;

    return $user;

List Online Users Shortcode

After we did all the hard work of storing the data about user on the database, now we will use that information to print an HTML with the list of users that are currently online.

public function shortcode_list( $atts ) {
    $atts = (object) shortcode_atts( array(
        'avatar' => false,

        'exclude' => '',
        'include' => '',
    ), $atts );

    $users = $this->get_users( $atts->include, $atts->exclude );

    $html = '<ul class="users-online">';
    foreach ( (array) $users as $user ) {
        $html .= '<li>';
        // Allow the user to control the avatar size and if he wants to show
        if ( is_numeric( $atts->avatar ) ){
            $html .= get_avatar( $user , $atts->avatar );
        $html .= '<span>' . $user->display_name . '</span>';
        $html .= '</li>';
    $html .= '</ul>';
    return $html;

Display the quantity of Users Online

The user might also want to display the quantity of users that are online with a shortcode, so we will deal with that too.

public function shortcode_qty( $atts ) {
    $atts = (object) shortcode_atts( array(
        'plural' => __( '%s users online', 'online-now' ),
        'singular' => __( 'One user online', 'online-now' ),
        'zero' => __( 'Zero users online', 'online-now' ),

        'numeric' => false,

        'exclude' => '',
        'include' => '',
    ), $atts );

    $users = $this->get_users( $atts->include, $atts->exclude );

    if ( $atts->numeric ){
        return count( $users );

    if ( count( $users ) === 0 ) {
        $text = $atts->zero;
    } elseif ( count( $users ) === 1 ) {
        $text = $atts->singular;
    } else {
        $text = $atts->plural;

    return sprintf( $text, count( $users ) );

Repository and Download

You can always checkout the oficial repository for this plugin and/or download the latest version of the code to install it in your WordPress.

How to make WordPress Database Case Insensitive

When I started to work with WordPress I didn't know anything about how databases works or anything related to encoding and character set, but as I started into adventure myself on places like pre_get_posts, and the WP_Query filters such as posts_join and posts_where, I quickly found that understanding how the database works was a key to unlocking better performance.

Once I was trying to do a search on some User meta data and I didn't know why one of my results where not been shown as I expected so delving further and debugging I found that there an information called Collation which is the set of Rules that your database table will follow.

The problem was this meta data was a city value, and I did not have control over the user input so it needed to be case-insensitive, which was not happening because the Collation was set to be utf8_bin that will make your MySQL compare queries that involve LIKE via a Binary structure so it will A is not equal to a.

This case sensibility issue on WordPress databases or any MySQL is easy to solve, you just need to change the collation of the tables that you want to be insensitive by executing the following SQL query on your database.

ALTER TABLE `wp_posts` CONVERT TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;
ALTER TABLE `wp_postmeta` CONVERT TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;

Where the _ci at the end will convert the Collation to be Case Insensitive, remember that changing the Collation of a table might lead you to have security problems of people trying to pose as Administrator account, which in WordPress is not the case because there are validations for that but if you are in another system you might want to double check.