Otto on WordPress

There’s been a lot of talk about custom post types, and I know many people are looking forward to it. Unfortunately, I think some (perhaps many) of those people are going to be disappointed. Custom Post Types might not be what you think they are.

I blame the naming, really. “Custom Post Types” makes the implication that these are “Posts”. They’re not. “Post Type” is really referring to the internal structure of WordPress. See, all the main content in WordPress is stored in a table called “wp_posts”. It has a post_type column, and until now, that column has had two main values in it: “post” and “page”. And there’s the big secret:

“Custom Post Types” are really Pages.

Sorta.

For a long time in the early days of WordPress, it just had Posts. But hey, no big deal, because it was just running a big Blog anyway, right? The Posts appeared on the Blog page (and in the Feed) in reverse chronological order. Each Post could appear on its own URL, using the Permalink structure.

Pages came along and changed that.

• Pages don’t appear on the Blog. Or in the Feed.
• Pages don’t even really have dates and times on them that usually get displayed.
• Pages have their own URL at the root of the website, outside the Permalink rules.
• Pages even have hierarchy in their URLs, if they want.

Pages, however, do live in the wp_posts table. So post_type exists to handle that. When WordPress is building the Blog, it looks for post_type = “post”.

Bring on the “Custom”.

Now we have these Custom Post Types. Or rather, custom post_types. Instead of “page” or “post”, we can have “custom”. Or “fred”. Whatever we like.

But how do these new post types get displayed? What do their URLs look like?

Well, these are custom, and they can be customized. You can give them their own space on the website. So if I want them to live at /custom/page-name, then I can. If I want them to have hierarchy, then I can do so. Justin Tadlock explains how they can be made to do this quite well.

But they are still not Posts.
They do not show up on the Blog.
They do not appear in the Feed.

This is a matter of definitions, really. See, the Blog is a reverse chronological order of the Posts. That it what it is defined to be. The Feed is basically the same thing, in feed form.

So all of you thinking of a custom “Podcast” post type, you’re in for a disappointment.

So what’s the big deal?

Well, all that said, custom types can have their own systems of doing things. They are custom, and as such, they are customizable.

If, for example, you wanted to have them appear on their own “blog” area, or in their own “feed”, then sure, that’s entirely doable. You can make a function to produce your custom feed. You can then call “add_feed” to add your feed. You can create single-type.php templates in your theme that will be used for your custom type. You could even make a “blog” out of your custom type.

And doing it the other way is possible too. You can adjust the “Blog” to show your type. You could change the “Feed” to show your type as well.

But these things are NOT the default way of doing things. There’s no code in there to do that, and there’s very likely not going to be. If you want your type in the Blog, in the Feed, then you have to do it yourself. The URL is NOT easy to customize and play around with. The rewrite system is unforgiving, and you have to stick within a set of rules for things to work well.

However, should you? Let’s say you make a “Podcast” custom type. You can go to the effort of putting them in the feeds and making them show special on the blog… but you could already do that with a “podcast” category. And it’s much easier to do a category and customize categories than custom types will ever be.

Something like 80% of the uses I’ve seen for “custom types” would be better served by making normal posts and using some existing method to separate them or to otherwise mark them as special.

So what are they good for?

What if you could install a forum on your site? bbPress is pretty good. But it could get all complicated to set up and such. Well, plugins are pretty easy. But all those forum posts have to go somewhere…

Custom Post Types is a way for plugins to define types of content for themselves.

A bbPress forum could store every post in the forum as its own custom post type quite easily.Or a wiki plugin could store each of its own pages as a custom post type. Things like that.

See, they’d get their own URL handling automatically, and they wouldn’t need weird database handling tricks.. It makes things much simpler and easier for those plugins to do their thing when they have the backend support for it in the core.

Some of you are thinking “Okay, so plugin authors can make better use of them. I won’t have to write a lick of code, I’ll just install a plugin that makes my type and handles the stuff for me.” And yeah, you can do that.

But then you’re wedded to that plugin. WordPress doesn’t know about your custom posts. If you remove the plugin, your custom posts are still there, but now they’re completely invisible. Can’t be pulled up, seen in the admin, the URLs all stop working…

Wrap it up, son…

Using custom post types right now is, for most people, a bad idea. Only specialized usages really exist for them… for now.

For the long term, WordPress will probably use them a lot more extensively. And plugins can make great use of them for all sorts of things. But you, as a user, probably don’t need to be messing with them. Not if you’re just creating a website or writing a blog. Not right now. Wait for the plugin and core development to catch up to the potential. Using them early leaves you open for a world of confusion and grief.

The Custom Background screen is easy to add to any theme

Quick and simple way to add the new custom background selector to your WordPress 3.0 theme.

add_custom_background();

Seriously. That’s it. Just add that to the theme’s functions.php file.

Details

Okay, so your theme does need to have the normal wp_head() call in it. For those of you more CSS inclined, this basically creates CSS code for the body and adds that code to the head output directly. Voila, your theme gets styled.

Note that you will need to also not define your own background stuff in the theme for this to work. If the user tries to put in a solid color background and you define an image background, then the color won’t work or be visible over your image. Best to not put anything background related onto the body at all, in fact.

Customization

For those more inclined to customize things, there’s actually three parameters you can use:

function add_custom_background($header_callback = '', $admin_header_callback = '', $admin_image_div_callback = '')

Each of these are references to a callback function. If you use them, then you need to define your own callback functions to replace the default ones.

The header_callback function is what builds and outputs the CSS. The function takes no parameters, but it can use get_background_image() and get_background_color() to retrieve the necessary information. From this information, the function should produce and output (echo) the necessary <style> block to show the image.

The admin_header_callback function is called in the head section of the admin side of things; in the Background section to be specific. The admin_image_div_callback is similar, called immediately after displaying “This is your current background” on that page, where the image is displayed. If used, the admin_image_div_callback replaces the display of the current background image, so you custom callback should produce that instead.

These two admin callbacks can be used to modify the Background admin page, to add custom text or information, etc.

But generally, most themes won’t need this level of customization. Just add the basic code to the theme and the defaults are good to go.

(Note to future readers: This is fixed in WordPress 3.3, so this article is now out-of-date. See http://core.trac.wordpress.org/changeset/18541 for the patch.)

I was not aware that other people didn’t know about this until recently, but since it seems to be little known, I thought I’d write a post on the topic.

In WordPress, you should never start the custom permalink string with any of these %postname%, %category%, %tag%, or %author%. (Unless you know what you’re doing, of course. )

Meaning that “%category%/%postname% ” is a bad custom permalink string. So is just “%postname%” for that matter.

Why? Well, it has to do with how the WordPress Rewrite system works.

Rewriting Explained

See, when you request a URL from a WordPress site, WordPress gets the URL and then has to parse it to determine what it is that you’re actually asking for.

It does this by using a series of rules that are built whenever you add new content to WordPress. Generally the list of rules is pretty small, but there are specific cases that can cause it to balloon way out of control.

Normal Rules

Let’s say you’re using a normal permalink string, like my preferred “%year%/%postname%”. The rules that are generated will look like this:

/robots.txt (for the privacy settings)
/feed/* (for normal feeds of any kind)
/comments/* (for comments feeds)
/search/* (pretty url for searches, not often used)
/category/%category% (category archives)
/tag/%tag% (tag archives)
/author/%author% (author archives)
/%year%/%month%/%day% (with each of those after year being optional)
/%year%/%postname% (this is the permalink string you define)
/%pagename% (any Page)

The way that system works is that it compares the URL it has to each of those in turn, from the top to the bottom. When one of them fits, then WordPress knows what to display and how to do it.

Note that the order I listed those in is is significant. Each one from the top down is less specific than the previous one.  For example, “robots.txt” matches only that, while “/feed/*” matches anything starting with /feed/. And so on down the list. The %postname%, %category%, %tag%, %author%, and %pagename% will match any string, but the other WordPress % ones will only match numeric fields. Like %year% is always a number.

Notice that the last one is %pagename%. This basically matches everything, because %pagename% can be anything at all. Even hierarchical pages like /plugins/whatever/something will cause this to match. It’s the fall-through position. And then, if that page doesn’t actually exist on your site, then this causes the query to trigger the 404 condition internally, which causes your theme’s 404.php to load up.

Pretty simple and straightforward, really.

Problem Rules

The problem comes in when you try to use a non-number for the beginning of your permalink string. Let’s examine those last two rules closer:

/%year%/%postname% (this is the permalink string you define)
/%pagename% (any Page)

What if you used “%category%/%postname%” for your custom permalink string? Now those last two rules are these:

/%category%/%postname% (this is the permalink string you define)
/%pagename% (any Page)

That violates our main rule, doesn’t it? That each one should be less specific than the one above it? Because %category% can match any string too, just like the %pagename% can… With this set of rules, there’s no way to view any of the Pages. Not good.

So, WordPress detects this condition and works around it. Internally, this sets a flag called “use_verbose_page_rules”, and that triggers the rewrite rebuild to make this set of rules instead:

/robots.txt (for the privacy settings)
/AAA
/BBB
/CCC (one of these for each of your Pages)
/feed/* (for normal feeds of any kind)
/comments/* (for comments feeds)
/search/* (pretty url for searches, not often used)
/category/%category% (category archives)
/tag/%tag% (tag archives)
/author/%author% (author archives)
/%year%/%month%/%day% (with each of those after year being optional)
/%category%/%postname% (this is the permalink string you define)

Now we have basically the same set of rules, except for those new ones at the top. Every Page now gets its own very specific rule, and this satisfies our main condition once again.

Pages

But what if you have a lot of Pages? I once read a post by a person who had over 50,000 Pages on his site. That is a special case obviously, but consider our lookup system. We’re going through these rules one at a time. With our first method, our rule list was only 10 rules, maximum. With this new method, you add a rule for every single Page you make. Going through 50,000 rules takes a lot longer than going through 10. And even just building that list of rules can take a long time.

Basically you’ve created a performance issue. Your Pages now won’t scale to unlimited numbers. Your site’s speed is linearly dependent on the number of Pages you have.

This is a bad thing.

Conclusion

Firstly, it’s really not any better for SEO to have the category in there, or to have just the postname there by itself. And anybody who tells you differently is wrong. If you disagree with me, then no, I’m not interested in arguing this point with you; you’re just wrong, period, end of discussion.

Secondly, shorter links are great and all, but hell, why not use a real shortlink? WordPress 3.0 now has a ShortLink API that defaults to using ?p=number links on your own domain. These will actually work for any WordPress site, even ye back unto WordPress 2.5. WordPress 3.0 just makes it nicer and easier to use these with the Shortlink API (as well as allowing plugins to make this automagically use services like wp.me or bit.ly). So use that instead.

The conclusion is, in general, just don’t do it. Leave a number, or something static, at the beginning of your permalink string and you’ll never have any sort of problems. But if you really MUST do this sort of thing, then keep your number of Pages low. Don’t try it when you have more than, say, 30-50 Pages.

Addendum

Okay, so I actually simplified things for this post. It’s actually worse than this, as verbose page rules can add much more than one rule per page, as this post demonstrates (he gets 11 per extra page!).