WordPress Software Development at H1. Part 3: Application Code

PostType classes

Since WordPress is a CMS, the most important thing is content. So let’s first look into what would a post type class look like.

namespace ProjectName\PostType;

 * Page, a WordPress default post type
class Page extends \WPlinth\PostType {

	const TYPE = 'page';

	public function set_registration_parameters() {

	public function set_meta_boxes() {


Both WordPress default post types, Page and Post, can be defined as a class that extends the WPlinth PostType class. This is not necessary, if your application does nothing to extend the functionality of those types. However, from the simplistic example above, we can see how a PostType class is constructed. We define the post type name as a class level constant. Then we have two functions, set_registration_parameters and set_meta_boxes that will be called automatically, if they are defined, by the base class. Below, you can see a more realistic example:

namespace ProjectName\PostType;

 * Service post type
 * Represents a service provided to a customer,
 * e. g. Project Management or Maintenance.
class Service extends \WPlinth\PostType {

	const TYPE = 'projectname_service';

	public function set_registration_parameters() {
		$this->labels = array( 
			'menu_name'          => __( 'Services', 'projectname-application' ),
			'name'               => _x( 'Services', 'post type general name', 'projectname-application' ),
			'singular_name'      => _x( 'Service', 'post type singular name', 'projectname-application' ),
			'name_admin_bar'     => _x( 'Service', 'add new on admin bar', 'projectname-application' ),
			'add_new'            => _x( 'Add New', 'service', 'projectname-application' ),
			'add_new_item'       => __( 'Add New Service', 'projectname-application' ),
			'new_item'           => __( 'New Service', 'projectname-application' ),
			'edit_item'          => __( 'Edit Service', 'projectname-application' ),
			'view_item'          => __( 'View Service', 'projectname-application' ),
			'all_items'          => __( 'All Services', 'projectname-application' ),
			'search_items'       => __( 'Search Services', 'projectname-application' ),
			'parent_item_colon'  => __( 'Parent Services:', 'projectname-application' ),
			'not_found'          => __( 'No services found.', 'projectname-application' ),
			'not_found_in_trash' => __( 'No services found in Trash.', 'projectname-application' ),

		 * Define other arguments
		$this->args = array(
			'rewrite'  => array( 'slug' => 'services' ),
			'supports' => array( 'title', 'editor', 'thumbnail', 'excerpt', 'revisions' ),

	public function set_meta_boxes() {
		$this->meta_boxes[] = array(
			'title' => 'Pricing',
			'pages' => array( self::TYPE ), // Array of post types
			'context'    => 'normal',
			'priority'   => 'high',
			'fields' => array(
					'id'   => 'projectname_service_hourly_price',
					'name' => __( 'Hourly price', 'projectname-application' ),
					'type' => 'text',
					'id'   => 'projectname_service_daily_price',
					'name' => __( 'Daily price', 'projectname-application' ),
					'type' => 'text',


In set_registration_parameters we do two things. First we set the labels to an instance variable labels. Then we do that for other arguments of register_post_type. The base class takes care of the rest.

In set_meta_boxes we append to the meta_boxes array the meta fields we would like our post type have. We use the format shared with plugins Custom Meta Boxes and Meta Box. One of those plugins should be active. If you would like to use something else, you can extend ProjectName\PostType and take care of that part yourself.

Taxonomy classes

Taxonomies work a lot the same way than post types. Below is a sample. It should be pretty self-explanatory.

namespace ProjectName\Taxonomy;

class CaseType extends \WPlinth\Taxonomy {
	const TAXONOMY = 'projectname_casetype';

	public function set_taxonomy_data() {

		$labels = array(
			'name'					=> _x( 'Case Type', 'Taxonomy plural name', 'projectname-application' ),
			'singular_name'			=> _x( 'Case Type', 'Taxonomy singular name', 'projectname-application' ),
			'search_items'			=> __( 'Search Case Types', 'projectname-application' ),
			'popular_items'			=> __( 'Popular Case Types', 'projectname-application' ),
			'all_items'				=> __( 'All Case Types', 'projectname-application' ),
			'parent_item'			=> __( 'Parent Case Type', 'projectname-application' ),
			'parent_item_colon'		=> __( 'Parent Case Type', 'projectname-application' ),
			'edit_item'				=> __( 'Edit Case Type', 'projectname-application' ),
			'update_item'			=> __( 'Update Case Type', 'projectname-application' ),
			'add_new_item'			=> __( 'Add New Case Type', 'projectname-application' ),
			'new_item_name'			=> __( 'New Case Type', 'projectname-application' ),
			'add_or_remove_items'	=> __( 'Add or remove Case Type', 'projectname-application' ),
			'choose_from_most_used'	=> __( 'Choose from most used Case Types', 'projectname-application' ),
			'menu_name'				=> __( 'Case Type', 'projectname-application' ),
		$args = array(
			'labels'            => $labels,
			'public'            => true,
			'show_in_nav_menus' => true,
			'show_admin_column' => true,
			'hierarchical'      => true,
			'show_tagcloud'     => true,
			'show_ui'           => true,
			'query_var'         => true,
			'rewrite'           => array( 'slug' => 'case-type' ),
			'query_var'         => true,

		$this->args = $args;

		$this->types = array( 'projectname_casestudy' );


Connection classes

If we want to define a Posts to Posts connection, we extend the \WPlinth\Connection class. Here is a simple example:

namespace ProjectName\Connection;

class ServicesProvided extends \WPlinth\Connection {

	const NAME = 'services_provided';

	protected $connection_type;

	public function set_connection_type() {
		$this->connection_type = array(
			'name'  => self::NAME,
			'from'  => 'projectname_casestudy',
			'to'    => 'projectname_service',
			'cardinality' => 'one-to-many',
			'title' => array(
				'from' => __( 'Casestudies', 'projectname-application' ),
				'to' => __( 'The Service', 'projectname-application' )

All the functionality that is related to the connection should be put into this class. We might, for example, want a function to fetch all the services provided for a case. That would look like something like this:

public function get_services( $casestudy_id ) {
		$services = p2p_get_connections(
			array( 'from' => $casestudy_id, 'to' => 'any' )
		return $services;

Even this simple function does make sense to exist, since this way we are able to encapsulate all the logic that is touching Posts 2 Posts API and thus keep all other code not dependant on that particular implementation. The code that would need to consume this function would need to have an instance of our ServicesProvided class. And, you guessed it, that instance would be provided to your consuming class by the DependencyInjection container, provided that you had defined the dependency in the configuration file.

QueryFilter classes

We are using QueryFilters to modify the main query for specific views. Instead of having a mess of unreadable if else statements, we define separate classes for each modification. Let’s look at an example. Say we wanted to display case studies in addition to posts on the front page.

namespace ProjectName\QueryFilter;

 * Display posts and case studies on front page
class FrontPage extends \WPlinth\QueryFilter {
	const PRIORITY = 10;

	public function test( $query ) {
		return $query->is_home();

	public function filter( $query ) {
		$query->set( 'post_type', array(

A QueryFilter consists of three parts. First, we can define a priority. Filters are tested in the order of their priority and only one filter is run per page load. Lower number means earlier execution.

QueryFilters in the system are tested first. The test function should return true, if the query does match the view WordPress is executing. In our example, we are simply testing weather WordPress thinks the current page is home page.

If the test matches, filter function is run. There we have the opportunity to do the modifications to the query we like.

Going further

These are just the most common ways of modifying and extending WordPress for a project specific way. If your application does something else, say, defines multiple shortcodes, it would make sense to create a base class for those and group them in a namespace/folder, in a similar fashion than what I have demonstrated above.

Other than that, this is it, a better way to organize your application code.

In the next part, we are going to discuss writing unit test.

WordPress Software Development at H1. Part 2: Application Structure

Application loader

Bedrock does give you a project structure, but for your own code, it is still just regular old plugins, mu plugins and themes. We like to place our project core code as an mu plugin, and we put inside a [appname]-application folder. If we come up with reusable functionality, we separate those as plugins and mu plugins.

We start our application up in a php file in mu-plugins directory. That file is called [appname]-loader.php and looks something like this:

namespace MyApplication;

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\Config\FileLocator;
use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;

// Initiate Composer Autoloading.
require( ABSPATH . '../../vendor/autoload.php' );

// Bootstrap other mu plugins.
require( 'posts-to-posts/posts-to-posts.php' );
require( 'cmb/Custom-Meta-Boxes/custom-meta-boxes.php' );

// Load application configuration.
$container = new ContainerBuilder();
$loader = new YamlFileLoader( $container,
	new FileLocator( __DIR__ . '/../../../config' ) );
$loader->load( 'services.yml' );

// Initiate the application.

What is happening there? To my taste, there is too much boilerplate code in there that would benefit of being encapsulated somewhere else. But, basically we just initiate the Symfony DependencyInjection container with a configuration file and then get an instance of our application class from it. Because of what we had defined in the configuration file, the application will get every object it will need from the container.

Application confuguration

Let’s look at the configuration file, services.yml. It has two parts. First, the parameters of each constructor is defined:

        - @post
        - @page
        - @person
        - @casestudy
        - @service
        - @case_personnel
        - @services_provided
        - @casetype
        - @expertise
        - @frontpage
        - @cases
        - @persons
        - @person_api
        - @auto_meta_property

Names starting with @ are references to classes, defined in the later part of the file. The parameters are arrays of classes.

Then, the actual services, which in practise means classes:

        class:     WPlinth\WordPressFactory
        class:     WPlinth\PostTypeManager
        arguments: ["%posttypes%"]
        class:     WPlinth\QueryFilterManager
        arguments: ["%queryfilters%"]
        class:     ProjectName\Application
            - "@post_type_manager"
            - "%connections%"
            - "%taxonomies%"
            - "@queryfiltermanager"
            - "%services%"
        class:     H1\Logging\Logging
        class:     ProjectName\PostType\Post
        class:     ProjectName\PostType\Page
        class:     ProjectName\PostType\Person
        arguments: ["@logging"]
        calls:     [[set_wp, ["@wordpress"]]]
        class:     ProjectName\PostType\CaseStudy
        calls:     [[set_wp, ["@wordpress"]]]
        class:     ProjectName\PostType\Service
        calls:     [[set_wp, ["@wordpress"]]]
        class:     ProjectName\Connection\CasePersonnel
        class:     ProjectName\Connection\ServicesProvided
        class:     ProjectName\Taxonomy\CaseType
        class:     ProjectName\Service\PersonAPI
        class:     WPlinth\AutoMetaProperty
        arguments: ["@post_type_manager"]
        class:     ProjectName\QueryFilter\FrontPage
        class:     ProjectName\QueryFilter\Cases
        class:     ProjectName\QueryFilter\Persons

This example file is from a fictitious project. Let me explain it a bit. We have a site that displays reference cases and services that a company has. Personnel and services are connected to reference cases with Posts to Posts. Personnel information is integrated with the company CRM, using PersonAPI class, and we are logging each change to a person post because of that.

Application class

An instance of most classes is passed on to the Application object as a parameter. That class itself can be very simple:

namespace ProjectName;

class Application {
	public function __construct( $posttypemanager, $connections,
		 $taxonomies, $querymanager, $services ) {

We could store the constructor parameters as instance variables, if we would like to extend the Application class to do stuff with those. But in normally we don’t have to.

Application folder structure

Our [appname]-application has a specific structure. Here is a typical directory structure:


Each of the folder contains the classes that inherit from a base class in WPlinth. For example PostType folder contains all the post types and they are classes that inherit from WPlinth PostType base class. Service is just a generic folder name for miscellaneous services. You can obviously have different and/or other folders (namespaces) in your application.

In the next post, we’ll look at code inside those classes.

WordPress Software Development at H1. Part 1: The Building Blocks

You have probably heard somebody say that it is impossible to write proper, professional software with WordPress. If not, at least somebody has implied how WordPress is not a professional tool and that real software developers would not use it.

They are all wrong. You can write great code and WordPress is not stopping you.

This series of posts will not explain in detail what are the principles of great code and what are the benefits of writing such code. But if you already know about them, it will teach you how to apply those principles in the WordPress world.

Great code?

So what is this great code? For me, it starts by not being procedural. Most of WordPress itself and its plugins is procedural. That kind of development style quickly leads to messy code, if you write more than just a couple of functions.

You want your code to be clean, easy to understand, testable, with minimum amount of dependencies within components, reusable, extendable… and conforming to all the other principles of great code. You can do all this in procedural code. But these things are way easier if you write object-oriented code.

Tools we use

To do all this fast, you need tools. Here are the tools we use to build applications on WordPress:

(1) Bedrock WordPress Stack is a stack of tools and a project structure. The most significant thing that it comes with is (2) Composer. Composer is a dependency manager, meaning you get to define the third party requirements your application has and Composer will get them for you. You give up automatic updates from within WordPress, but for proper software development and maintenance process you should anyway.

Composer comes with (3) an implementation of PHP autoloading. Autoloading loads files that contain classes right when you need them. There is no need to litter the code with require and include statements. Autoloading requires you to name the folders and files according to a strict standard, which in itself is a good thing. Folders match the namespace names and file names match the class names they contain.

There are some very common types of classes we write. Probably the most common type is a class that represents a custom post type. Custom taxonomies, Posts 2 Posts connections and query filters are other common types. To help with that, we have created (4) WPlinth, a collection of base classes and other functionality. It helps with writing testable code in other ways too: there is a simple mechanism to easily mock WP_Query and other core WordPress classes without using a wrapper.

As part of WPlinth we have adopted and modified (5) Loopable Query to let us interact with WP_Queries with foreach loops and not all that boilerplate code you normally have to deal with. Turns out that makes mocking the monstrous WP_Query a lot easier, since in many cases you can use an array to do the job, and in worst cases you need to cast that array as an object.

We use Symfony framework’s (6) DependencyInjection Component. Dependency injection helps to write code that is not dependent of specific implementation of other functionality. We define our application class configuration as a yml file and could easily switch the implementation of parts of the application without actually touching the code.

For writing the actual tests, we use (7) PHPUnit. To help with WordPress specific testing we use (8) WP_Mock.

Every tool I mentioned above, except of course Bedrock, is available as a Composer package.

In the next post we will delve into actual code and more details of our setup.