WordPress Plugin Development : Invoice Management


We are starting a WordPress plugin development project to Create a complete WordPress plugin that involves management and has multiple files and components. Here’s a simplified example of an Invoice Management plugin with database submission. Please note that this example uses the WordPress database directly for simplicity. In a real-world scenario, you should consider using WordPress APIs and best practices for data handling.

File Structure for Invoice Management Plugin:

|-- invoice-management.php
|-- includes/
| |-- invoice-functions.php
| |-- admin.php
| |-- front-end.php
|-- css/
| |-- style.css
|-- js/
| |-- script.js
|-- templates/
| |-- admin-invoice-form.php
| |-- front-end-invoices.php
|-- README.md


Let’s break down each of these components:

  1. invoice-management-plugin/: This is the main plugin folder that holds all your plugin files and directories.
  2. invoice-management.php: The main plugin file contains plugin metadata, such as name, description, version, and author. It also includes references to other necessary files and sets up constants.
  3. includes/: This directory holds various functional components of the plugin.
    • invoice-functions.php: This file contains functions for invoice-related operations, such as creating invoices and retrieving invoice data from the database.
    • admin.php: Handles the administrative interface for managing invoices. It adds a menu item in the WordPress admin panel and defines functions to manage the display and submission of invoices in the admin area.
    • front-end.php: Manages the front-end display of invoices. It contains functions to retrieve and display invoices on the website’s front end.
  4. css/: This directory would hold any stylesheets associated with your plugin.
    • style.css: This file would contain the CSS styles used to style the front-end display of invoices.
  5. js/: This directory would hold any JavaScript files associated with your plugin.
    • script.js: This file would contain JavaScript code if your plugin requires client-side interactivity.
  6. templates/: This directory contains template files for rendering content in the admin and front-end areas.
    • admin-invoice-form.php: This file defines the HTML structure for the invoice submission form in the admin panel.
    • front-end-invoices.php: This file defines the HTML structure for displaying invoices on the website’s front-end.
  7. README.md: This file can contain documentation for your plugin, explaining its features, usage, and any other relevant information.

This file structure is a basic example. In a real-world scenario, you might have additional directories, files, and assets depending on the complexity of your plugin’s functionality. Additionally, consider adhering to WordPress coding standards and best practices for naming, organizing, and structuring your files and code.

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WordPress Plugin Development: Step By Step

1. Create a folder for your plugin: Create a folder named invoice-management-plugin in the wp-content/plugins directory of your WordPress installation.

2. Create the main plugin file: Inside the invoice-management-plugin folder, create a main PHP file, e.g., invoice-management.php.

Plugin Name: Invoice Management
Description: Manage invoices in WordPress.
Version: 1.0
Author: Your Name

// Define constants
define('INVOICE_MANAGEMENT_PLUGIN_DIR', plugin_dir_path(__FILE__));

// Include necessary files
require_once INVOICE_MANAGEMENT_PLUGIN_DIR . 'includes/invoice-functions.php';
require_once INVOICE_MANAGEMENT_PLUGIN_DIR . 'includes/admin.php';
require_once INVOICE_MANAGEMENT_PLUGIN_DIR . 'includes/front-end.php';

3. Create the includes directory: Inside the invoice-management-plugin folder, create a includes directory. This is where you’ll place various functional components.

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4. Create invoice-functions.php: This file will contain functions for invoice-related operations.

// Create invoice
function create_invoice($amount, $customer_name, $due_date) {
global $wpdb;
$table_name = $wpdb->prefix . 'invoices';

'amount' => $amount,
'customer_name' => $customer_name,
'due_date' => $due_date,

// Get list of invoices
function get_invoices() {
global $wpdb;
$table_name = $wpdb->prefix . 'invoices';
return $wpdb->get_results("SELECT * FROM $table_name", ARRAY_A);

5. Create admin.php: This file will handle the administration interface for managing invoices.

// Add menu item for invoices
function invoice_management_menu() {
'Invoice Management',
'Invoice Management',
add_action('admin_menu', 'invoice_management_menu');

// Invoice management page
function invoice_management_page() {
if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['submit_invoice'])) {
$amount = sanitize_text_field($_POST['amount']);
$customer_name = sanitize_text_field($_POST['customer_name']);
$due_date = sanitize_text_field($_POST['due_date']);

create_invoice($amount, $customer_name, $due_date);

// Display the invoice submission form
include_once INVOICE_MANAGEMENT_PLUGIN_DIR . 'templates/admin-invoice-form.php';

6. Create front-end.php: This file will handle the display of invoices on the front-end of your website.

// Display invoices on the front-end
function display_invoices() {
$invoices = get_invoices();

// Display the invoices on the front-end
include_once INVOICE_MANAGEMENT_PLUGIN_DIR . 'templates/front-end-invoices.php';

7. Create templates folder: Inside the invoice-management-plugin folder, create a templates folder to store your template files.

8. Create template files: Inside the templates folder, create admin-invoice-form.php and front-end-invoices.php to define your form and front-end display layouts.

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9. Activate the plugin: Go to the WordPress admin panel, navigate to the “Plugins” section, and activate your “Invoice Management” plugin.

Remember that this is a simplified example. You should sanitize and validate user input, handle form submissions securely, and apply WordPress best practices. Also, consider using the WordPress Database API instead of direct SQL queries for better security and compatibility.

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