Why does WP_Post not contain its permalink?

Question

When I do something like:

$prevPost = get_previous_post();

I can then do:

$prevPost->post_title;
$prevPost->post_content;
...

Why can't I get the permalink?

$prevPost->post_url; // NULL
$prevPost->post_permalink; // NULL

Obviously, as stated in the codex, that class doesn't have these properties. However, it seems logical to have the post URL as part of the post. Why is that not the case?

To get the permalink, I need to do:

get_permalink($prevPost);

But then, I can't do something like this to get the title:

get_title($prevPost);

Questions

What's the reason for these inconsistencies? Why do I have to get some of the post data via the post object and other - with the get functions? I'm relatively new to WordPress, so an article explaining it all would be much appreciated.
Are there any other types of data that share these inconsistencies? What are they?

Jacob Peattie · Accepted Answer

WP_Post is a representation of the post as it exists in the database, and the permalink isn't stored in the database.

It's not stored in the database because it's not a property of the post. The permalink is determined by the site's address, its permalink structure, and the post's slug. Imagine if updating the permalink structure on your site required that every post in the database had to be updated.

But then, I can't do something like this to get the title:
  
  get_title($prevPost);

You can

get_the_title($prevPost);

For consistency's sake, you can also do:

get_the_permalink($prevPost);

user193213 · Answer

Try
the_permalink($post_object->ID);

Milo · Answer

While it's possible to access post content directly from the post object, you should not do this. All data should be accessed via the API functions- title, content, etc., so all applicable filters will be applied. Accessing data directly will break formatting and many plugin functions.

Answered by Milo on January 14, 2021

Why does WP_Post not contain its permalink?

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