WordPress Plugin Bootstrap Files and Class Architecture

I’ve been casually working on my Board Game Collector plugin off and on for awhile. It’s a fairly basic plugin that registers a custom settings page, post type, and WP-CLI command that allows you to connect to the BoardGameGeek API to pull in data for a given user’s board game collection. I’m still undecided as to the long-term utility of the plugin, so when I work on it, it becomes a playground of sorts for me to try out ideas.

A couple of months ago, I completely refactored the plugin to take advantage of the OOPS-WP library I had written for WebDevStudios, because I wanted it to more closely follow the style I’d established over the years for WordPress projects. This morning, after revisiting it once more, I decided I didn’t fully like the structure of the plugin bootstrap file, so I made a few minor tweaks. I’ve never actually written my approach down anywhere, so I figured a rainy day like today was as good as any to talk about my coding philosophy when it comes to plugin bootstrap files and class file organization.

Anatomy of a Plugin Bootstrap File

First, let’s take a look at the plugin bootstrap file for the Board Game Collector plugin is it exists in the develop branch of the repository this morning:

The main thing to notice here is that I’ve established that the sole responsibility of the bootstrap file is to determine whether WordPress can locate the files it needs to run. Any further plugin behavior is delegated to the main plugin file where services are instantiated, hooks are registered, constants are defined, and so on. Since I’m using Composer for class autoloading, I do want WordPress to check whether that autoloader exists locally within the plugin in case I installed it directly instead of requiring it via composer install somewhere from within the WordPress project.

One thing I changed this morning was moving toward the use of a try/catch block when attempting to initialize the plugin class. Previously, I was running a class_exists check to determine whether or not the plugin can run. But, in working with some enterprise WordPress multisite projects, I’ve come to learn that – depending on the particular configuration – class_exists might return true for a plugin that is deactivated on one site but active on another. In those projects, we had circumvented that behavior by passing in false as the second parameter to class_exists, but I think this try/catch approach is more explicit. If the class files are not loaded, then my plugin will catch the error and handle the notification/deactivation process.

And that, in a nutshell, is the entirety of the bootstrap process. Just about every plugin I write nowadays incorporates some version of this structure:

1. Check for the presence of a local autoloader
2. Try to instantiate the main plugin class on the plugins_loaded action and run it.
3. Display a notice and deactivate the plugin if anything went wrong.

Class File Organization

Next, let’s take a look at the file structure for this particular plugin.

By adhering to the PSR-4 standard for class autoloading, I’m able to organize the various classes that power my plugin into groupings relevant to their responsibilities. All class files at the root of the src/ directory have a namespace of JMichaelWard/BoardGameCollector, and from there, the namespace matches the relative path to the file. So, for instance, my CliService class, located at src/UI/Cli/, has a namespace of JMichaelWard/BoardGameCollector/UI/Cli.

The benefits of this approach are two-fold. First, when I need to make a change to a particular part of the plugin – say, updates to the API connections – I know exactly where I need to go, because everything is organized into top-level directories that describe what they are responsible for. Second, any classes referenced outside of that grouping can be easily located, because their namespace matches the file structure.

Today, many WordPress plugins still rely on a flat class structure which, sure, makes it easy to locate all of the class files, but I find that understanding the relationships between classes is far more challenging. This particular approach works for me, and perhaps it will work for you, too.

The Main Plugin File

Finally, let’s check out the main plugin file and see how things are structured.

There’s kind of a lot going on here, but in many ways, the main class file is a lot like the bootstrap file. Its job is to define a set of “services” – basically, processes for which the plugin is responsible for starting up – and make sure that those services are run. At this point in time, the Board Game Collector plugin has 5 primary services:

• A ContentRegistrar, which is responsible for registering custom post types and taxonomies with WordPress.
• An ApiService, which is responsible for registering custom API endpoints within WordPress and for communicating with the BoardGameGeek API.
• A CliService, which is responsible for registering custom WP-CLI commands.
• A CronService, which is responsible for setting up tasks that need to trigger at given intervals.
• The Settings service, which is responsible for registering admin interfaces for working with the plugin inside of the WordPress dashboard.

Beyond that functionality, there are a few additional things I’d like to point out in this class file.

First, I’m using a Dependency Injection container called Auryn in this project. Auryn is, simply put, completely magical. On line 79 of the gist, the call to $this->injector->make passes in the current service class name to Auryn and leaves the instantiation of that object to it. If the class defines any other classes within its constructor, Auryn will load an existing instance of it if it finds one, otherwise, it will instantiate that dependency for you. The benefit is that your class constructors can be properly defined with the actual objects your class needs, making it easier to understand later what an object is made of. Auryn probably deserves a whole separate blog post of its own, so I’ll leave it at that for now.

Second, within the register_services method, I’m calling array_column on the resulting set of services and reassigning it to the $services property. This turns the indexed array into an associative array instead, and allows me – should I need it – to request a particular service object by its class name.

Lastly, after each of the service objects are instantiated, I pass the actual services to a register_service method, which passes in the main plugin file path to the objects that require it, and finally, calls their run methods to trigger the processes for those services. The benefit here is that register_service is type-hinted to the Service abstract class in OOPS-WP, meaning that if I add a service class name to the array inside of th main class, but forget to actually extend the abstract class, PHP will throw a fatal error. Errors are extremely helpful when attempting to abide by a given standard, and putting these guardrails in place for myself overtime have made me a better developer and made my own code a little more foolproof.

Summary

Hopefully this post gives you some ideas about approaches you can take to structure your own projects. I absolutely love working with object oriented code, and I’m hoping that as time goes on, we start to see more WordPress developers incorporating object-oriented practices into their plugins and themes. Clearly separating the responsibility of your code into sections, as I’ve demonstrated above, can make it easier for other engineers (or even your future self!) to understand what’s going on within your application, thereby reducing the time it takes to make fixes or to create brand new features.

If you happened to read this post and found it helpful or informative, please give me a shout on Twitter and let me know!