I'd like to create a subclass of WP_Post and add some "model functionality" to it. How can i force WP to create objects of that child class instead of WP_Post itself, when i query for my custom post type?


Let's assume i have two custom post types: Book and Review. Each Book can have many Reviews. On my Book, I want a method to sum up all its reviews. I'd define the following class:

class Book extends WP_Post
    public function reviewsSummary()
        // Retrieve all reviews for $this book
        // Sum up their ratings
        // Return that sum

Is there a way, for example when calling register_post_type(), to force WordPress into casting all posts of type "book" into my Book class instead of WP_Post?

Could look something like this:

register_post_type('book', [
    'class' => Acme\Models\Book::class
  • I like the idea of asking register_post_type to return you own class instead of the wp_post class. But no that functionality does not exist in the current class. Nov 18, 2016 at 3:55
  • You might want to use a Decorator if you need to extend the functionality or a Proxy if you need to get an layer of abstraction for refactoring and decoupling (not for gaining access to private or protected functions!). You could as well build a factory and some repository where you can return whatever pleases your needs. WP_Post is rarely needed directly in cases where you do not have to rely on checks against a concrete type.
    – kaiser
    Nov 22, 2016 at 21:59
  • Btw people with similar questions might be interested in Timber: timber.github.io/timber
    – jsphpl
    Nov 25, 2016 at 10:27

2 Answers 2


WP_Post class in WP is final, so it explicitly forbids subclassing. It is also quite vague in practice, a lot of code around will happily take/produce post–like objects as long as they have established data structure.

It is challenging to recommend an alternative without knowing more about your specific needs. In a general and assuming use in templates the typical would be to create a template tag function that will calculate score for review post, provided to it as argument and/or current in the Loop.


How to "subclass" WP_Post

Thank you, @Rarst for pointing out the issue that you can't subclass WP_Post, which is a major problem in this case.


There is, however, a way of working around it using a wrapper class that has a real WP_Post object stored as an attribute and exposes it via magic methods in order to behave like one.

Two examples of that approach can be found here and here.

Warning: In many cases, this approach might not work for different reasons, one being that these objects won't pass an instanceof WP_Post check.

Where to hook in

So let's assume we could replace WP_Post somehow. The thing i was actually looking for was where to hook in in order to replace WP_Post. The answer to this question is the posts_results filter and was given here: https://stackoverflow.com/a/40631962/3919281

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