My Wordpress Collection

Navigate to the WordPress installation’s wp-content directory.
Open the plugins directory.
Create a new directory and name it after the plugin (e.g. plugin-name).
Open the new plugin’s directory.
Create a new PHP file (it’s also good to name this file after your plugin, e.g. plugin-name.php).

you’ll need to add a plugin header comment. This is a specially formatted PHP block comment that contains metadata about the plugin, such as its name, author, version, license, etc. The plugin header comment must comply with the header requirements, and at the very least, contain the name of the plugin.

<?php
/**
 * Plugin Name: YOUR PLUGIN NAME
 */

<?php
/**
 * Plugin Name:       My Basics Plugin
 * Plugin URI:        https://example.com/plugins/the-basics/
 * Description:       Handle the basics with this plugin.
 * Version:           1.10.3
 * Requires at least: 5.2
 * Requires PHP:      7.2
 * Author:            John Smith
 * Author URI:        https://author.example.com/
 * License:           GPL v2 or later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 * Text Domain:       my-basics-plugin
 * Domain Path:       /languages
 */

The deactivation hook is sometimes confused with the uninstall hook. The uninstall hook is best suited to delete all data permanently such as deleting plugin options and custom tables, etc.

Activation

register_activation_hook( __FILE__, 'pluginprefix_function_to_run' );

Deactivation

register_deactivation_hook( __FILE__, 'pluginprefix_function_to_run' );

The first parameter in each of these functions refers to your main plugin file, which is the file in which you have placed the plugin header comment. Usually these two functions will be triggered from within the main plugin file; however, if the functions are placed in any other file, you must update the first parameter to correctly point to the main plugin file.

Wordpress WP_Query Tutorial for beginners from scratch (Part#1) | About WP_Query and standard use

Video Tuts series by Online Web Tutor - Dec 30, 2018

// WP_Query which displays posts from movies category:
$the_query = new WP_Query( 'category_name=movies' );
 
// The Loop
if ( $the_query->have_posts() ) {
        echo '<ul>';
    while ( $the_query->have_posts() ) {
        $the_query->the_post();
        echo '<li>' . get_the_title() . '</li>';
    }
        echo '</ul>';
} else {
    // no posts found
}
/* Restore original Post Data */
wp_reset_postdata();

github.com/sultann/wp-query-builder/>

pressidium.com/blog/create-wordpress-custom-post-types-manually/

pressidium.com/blog/wordpress-custom-post-types-taking-it-further/

pressidium.com/blog/create-wordpress-custom-post-types-using-your-own-plugin/

Add a top-level menu page:

General Functions

Menu Pages

Submenu Pages

Wordpress Administration Menus

add_menu_page( 
	string $page_title, 
	string $menu_title, 
	string $capability, 
	string $menu_slug, 
	callable $function = '', 
	string $icon_url = '', 
	int $position = null 
	)

page_title: The title of the page.
menu_title: Menu title that will be displayed on the dashboard.
capability: Minimum capability to view the menu.
menu_slug: Unique name used for the menu item.
function:  Used to display page content.
icon_url: URL to custom image used as an icon.
position: Location in the menu order.

This function takes a capability which will be used to determine whether or not a page is included in the menu. The function which is hooked in to handle the output of the page must check that the user has the required capability as well.

Parameters

$page_title

(string) (Required) The text to be displayed in the title tags of the page when the menu is selected.

$menu_title

(string) (Required) The text to be used for the menu.

$capability

(string) (Required) The capability required for this menu to be displayed to the user.

$menu_slug

(string) (Required) The slug name to refer to this menu by. Should be unique for this menu page and only include lowercase alphanumeric, dashes, and underscores characters to be compatible with sanitize_key().

$function

(callable) (Optional) The function to be called to output the content for this page.

Default value: ''

The function that displays the page content for the menu page.

Technically, the function parameter is optional, but if it is not supplied, then WordPress will basically assume that including the PHP file will generate the administration screen, without calling a function. The page-generating code can be written in a function within the main plugin file.

In the event that the function parameter is specified, it is possible to use any string for the menu_slug parameter. This allows usage of pages such as ?page=my_super_plugin_page instead of ?page=my-super-plugin/admin-options.php.

The function must be referenced in one of two ways:

if the function is a member of a class within the plugin it should be referenced as array( $this, 'function_name' )
in all other cases, using the function name itself is sufficient

$icon_url

(string) (Optional) The URL to the icon to be used for this menu.
* Pass a base64-encoded SVG using a data URI, which will be colored to match the color scheme. This should begin with 'data:image/svg+xml;base64,'.
* Pass the name of a Dashicons helper class to use a font icon, e.g. 'dashicons-chart-pie'.
* Pass 'none' to leave div.wp-menu-image empty so an icon can be added via CSS.

Default value: ''

$position

(int) (Optional) The position in the menu order this one should appear.

Default value: null

Menu Structure:

To add an administration menu, you must do three things:

Create a function that contains the menu-building code
Register the above function using the admin_menu action hook. (If you are adding an admin menu for the Network, use network_admin_menu instead).
Create the HTML output for the page (screen) displayed when the menu item is clicked

It is that second step that is often overlooked by new developers. You cannot simply call the menu code described; you must put it inside a function, and then register the function.

Add Submenu page

add_submenu_page( 
			string $parent_slug, 
			string $page_title, 
			string $menu_title, 
			string $capability, 
			string $menu_slug, 
			callable $function = '' 
			)

Slugs for $parent_slug (first parameter)

Dashboard: ‘index.php’
Posts: ‘edit.php’
Media: ‘upload.php’
Pages: ‘edit.php?post_type=page’
Comments: ‘edit-comments.php’
Custom Post Types: ‘edit.php?post_type=your_post_type’
Appearance: ‘themes.php’
Plugins: ‘plugins.php’
Users: ‘users.php’
Tools: ‘tools.php’
Settings: ‘options-general.php’
Network Settings: ‘settings.php’

For Dashboard: add_submenu_page('index.php',...)
For Posts: add_submenu_page('edit.php',...)
For Media: add_submenu_page('upload.php',...)
For Pages: add_submenu_page('edit.php?post_type=page',...)
For Comments: add_submenu_page('edit-comments.php',...)
For Custom Post Types: add_submenu_page('edit.php?post_type=your_post_type',...)
For Appearance: add_submenu_page('themes.php',...)
For Plugins: add_submenu_page('plugins.php',...)
For Users: add_submenu_page('users.php',...)
For Tools: add_submenu_page('tools.php',...)
For Settings: add_submenu_page('options-general.php',...)

Determining Location for New Menus

Adding a submenu page to a custom post type

If you want to add a submenu type to a custom post type, such as a reference page for a custom post type created by a plugin, you can use for the $parent_slug parameter whatever you see up top on the “All Posts” view for that post type. For instance, for a custom post type “Book,” the $parent_slug could be 'edit.php?post_type=book'.

/**
 * Adds a submenu page under a custom post type parent.
 */
function books_register_ref_page() {
    add_submenu_page(
        'edit.php?post_type=book',
        __( 'Books Shortcode Reference', 'textdomain' ),
        __( 'Shortcode Reference', 'textdomain' ),
        'manage_options',
        'books-shortcode-ref',
        'books_ref_page_callback'
    );
}
 
/**
 * Display callback for the submenu page.
 */
function books_ref_page_callback() { 
    ?>
    <div class="wrap">
        <h1><?php _e( 'Books Shortcode Reference', 'textdomain' ); ?></h1>
        <p><?php _e( 'Helpful stuff here', 'textdomain' ); ?></p>
    </div>
    <?php
}

Submenu with PHP Class

/**
 * Sub menu class
 */
class Sub_menu {
 
    /**
     * Autoload method
     * @return void
     */
    public function __construct() {
        add_action( 'admin_menu', array(&$this, 'register_sub_menu') );
    }
 
    /**
     * Register submenu
     * @return void
     */
    public function register_sub_menu() {
        add_submenu_page( 
            'options-general.php', 'Submenu title', 'Submenu title', 'manage_options', 'submenu-page', array(&$this, 'submenu_page_callback')
        );
    }
 
    /**
     * Render submenu
     * @return void
     */
    public function submenu_page_callback() {
        echo '<div class="wrap">';
        echo '<h2>Submenu title</h2>';
        echo '</div>';
    }
 
}
 
new Sub_menu();


//absolute path to wp-load.php, or relative to this script
//e.g., ../wp-core/wp-load.php
include( 'trunk/wp-load.php' ); 

//grab the WPDB database object, using WP's database
//more info: http://codex.wordpress.org/Class_Reference/wpdb
global $wpdb;

//make a new DB object using a different database
//$mydb = new wpdb('username','password','database','localhost');

//basic functionality

//run any query
$wpdb->query( "SELECT * FROM wp_posts" );

//run a query and get the results as an associative array
$wpdb->get_results( "SELECT * FROM wp_posts" );

//get a single variable
$wpdb->get_var( "SELECT post_title FROM wp_posts WHERE ID = 1" );

//get a row as an assoc. array
$wpdb->get_row( "SELECT * FROM wp_posts WHERE ID = 1" );

//get an entire column
$wpdb->get_col( "SELECT post_title FROM wp_posts" );

Plugin Development

Tutorials & Developer Docs+

Knowledgebase+

Activation

Deactivation

WP_Query+

Admin Menu+

Add a top-level menu page:

Menu Pages

Submenu Pages

Parameters

Menu Structure:

Add Submenu page

Determining Location for New Menus

Adding a submenu page to a custom post type

Submenu with PHP Class

The wpdb Class+

WP_List_Table+

How to Load WordPress Post With AJAX+

How To Set Featured Image Programmatically In WordPress+

React with Wordpress+

Wordpress API & WP REST API+