Would you like to add new custom fields to your WordPress posts, pages, and categories? Now you can easily do this with the WordPress custom taxonomy system. For example, if you have a blog on music reviews, you may want to add the fields Artist and Genre to each of your posts. Here is an example movie blog that showcases the power of custom taxonomies.
What is less clear, however, is how you can expand your WordPress admin interface, so that users can easily enter in these new custom fields. WordPress 2.8+ will only include an input interface for custom taxonomies associated with posts. In addition, this input interface is the standard tag interface, where you must type in the new fields as plain text.
If you are looking for a drop-down menu, or a radio button list, you are out of luck.
Here, we consider how you can flexibly expand your WordPress post interface and style your custom taxonomy input panel however you want.
Screen-shot of the tag input interface associated with all custom taxonomies.
1. Create Your WordPress Custom Taxonomy
First, we create a simple test attribute called theme and we associate it with our WordPress posts. We add three initial terms to our new theme attribute – Beauty, Halloween, and Dragons.
Note that the hierarchical argument simply refers to whether your new theme attribute is a hierarchical structure, such as your WordPress categories, or whether it is flat, such as your WordPress tags.
The hierarchical argument does not currently affect the input interface of your new attribute. As of WordPress 2.8, the normal tag input interface will be used for all custom taxonomy attributes. To restyle the custom taxonomy input interface, you must use the add_meta_box command.
1 2 3 4 5 6 7 8 9 10 11 | add_action( 'init', 'create_theme_taxonomy', 0 ); function create_theme_taxonomy() { if (!is_taxonomy('theme')) { register_taxonomy( 'theme', 'post', array( 'hierarchical' => false, 'label' => __('Theme'), 'query_var' => 'theme', 'rewrite' => array( 'slug' => 'theme' ) ) ); wp_insert_term('Beauty', 'theme'); wp_insert_term('Dragons', 'theme'); wp_insert_term('Halloween', 'theme'); } } |
2. Styling Your Custom Taxonomy Input
To add input menus to your WordPress post interface, you want to use the WordPress add_meta_box command. In the example code below, we add a new custom field called Theme into our WordPress post interface. Simply include the code into your functions.php theme or plugin file.
1 2 3 4 5 6 7 8 9 10 11 12 13 | function add_theme_box() { add_meta_box('theme_box_ID', __('Theme'), 'your_styling_function', 'post', 'side', 'core'); } function add_theme_menus() { if ( ! is_admin() ) return; add_action('admin_menu', 'add_theme_box'); } add_theme_menus(); |
Screen-shot of your new drop-down custom taxonomy interface.
The add_meta_box function adds your_styling_function to the WordPress blog system so that it gets called whenever the Edit Post screen is rendered. You can use the same function to add input code to Edit Page and Edit Link screens.
The example your_styling_function below will add a drop-down menu to your blog Edit Post screen, containing all the current terms on your theme custom taxonomy. We use the ‘hide_empty=0‘ argument for the get_terms function on line 9, so that all theme choices will be returned, even the ones that have not yet been assigned to any post.
On line 15 we use the wp_get_object_terms function to get the theme currently associated with our post so that we may pre-select it in our drop-down menu.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | // This function gets called in edit-form-advanced.php
function your_styling_function($post) {
echo '<input type="hidden" name="taxonomy_noncename" id="taxonomy_noncename" value="' .
wp_create_nonce( 'taxonomy_theme' ) . '" />';
// Get all theme taxonomy terms
$themes = get_terms('theme', 'hide_empty=0');
?>
<select name='post_theme' id='post_theme'>
<!-- Display themes as options -->
<?php
$names = wp_get_object_terms($post->ID, 'theme');
?>
<option class='theme-option' value=''
<?php if (!count($names)) echo "selected";?>>None</option>
<?php
foreach ($themes as $theme) {
if (!is_wp_error($names) && !empty($names) && !strcmp($theme->name, $names[0]->name))
echo "<option class='theme-option' value='" . $theme->name . "' selected>" . $theme->name . "</option>\n";
else
echo "<option class='theme-option' value='" . $theme->name . "'>" . $theme->name . "</option>\n";
}
?>
</select>
<?php
} |
Screen-shot of the Edit Post, which now has the old tag input box and the new drop-down menu box.
Note that when you add your new drop-down menu box, the old tag input box will still appear. To only include one input box, use the remove_meta_box command as suggested by Leo Mysor in the comments section below.
remove_meta_box('tagsdiv-theme','post','core');
You can add the remove_meta_box command before your add_meta_box statement.
Alternatively, you can register your custom taxonomy attribute to something other than ‘post’. In the code example below, we register our theme custom taxonomy to shiba_post, which gets rid of the standard tag input box in the Edit Post screen.
register_taxonomy( 'theme', 'shiba_post', array( 'hierarchical' => false, 'label' => __('Theme'), 'query_var' => 'theme', 'rewrite' => array( 'slug' => 'theme' ) ) );
However, as pointed out by Leo, this also removes your taxonomy tab from the Posts menu and makes it difficult for others to add new items to your taxonomy.
3. Saving Your New Inputs
Now, we can insert any input panel we want for our custom taxonomy, however, we still need a way to save those input values. This can be achieved with the save_post WordPress hook. This hook allows you to execute a function of your choice when a WordPress post gets saved. There are similar hooks for saving pages and links.
Just add the save_post hook to your existing add_theme_menus function. For example, the code below registers the save_taxonomy_data function with the WordPress blog system so that it gets executed whenever a WordPress post is saved or updated.
1 2 3 4 5 6 7 8 9 10 | function add_theme_menus() { if ( ! is_admin() ) return; add_action('admin_menu', 'add_theme_box'); /* Use the save_post action to save new post data */ add_action('save_post', 'save_taxonomy_data'); } |
Now, you just need to specify your save_taxonomy_data function. We can adapt our own save function from the add_meta_data example on WordPress.org.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | function save_taxonomy_data($post_id) { // verify this came from our screen and with proper authorization. if ( !wp_verify_nonce( $_POST['taxonomy_noncename'], 'taxonomy_theme' )) { return $post_id; } // verify if this is an auto save routine. If it is our form has not been submitted, so we dont want to do anything if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE ) return $post_id; // Check permissions if ( 'page' == $_POST['post_type'] ) { if ( !current_user_can( 'edit_page', $post_id ) ) return $post_id; } else { if ( !current_user_can( 'edit_post', $post_id ) ) return $post_id; } // OK, we're authenticated: we need to find and save the data $post = get_post($post_id); if (($post->post_type == 'post') || ($post->post_type == 'page')) { // OR $post->post_type != 'revision' $theme = $_POST['post_theme']; wp_set_object_terms( $post_id, $theme, 'theme' ); } return $theme; } |
Lines 4-6 – First we do a nonce check to ensure that the function is being called by our very own your_styling_function. Make sure that the ‘taxonomy_noncename‘ and ‘taxonomy_theme‘ terms match those that were created earlier, on lines 4-5 in your_styling_function.
Lines 9-10 – Take no action for auto-saves.
Lines 14-20 – Check that the current user has proper permissions to edit posts.
Lines 23-28 – Associates our post with the new theme taxonomy data. It is important to do a post_type check here, because this function will also get called on post ‘revision‘ objects.
As pointed out by Angelia, this results in double counting the newly added taxonomy relationship.
4. Getting a Taxonomy Term Count
If you want to get the count of a particular taxonomy term, i.e., the number of objects that it is associated with, you can easily extract that figure from the WordPress term_taxonomy database.
Just add the count code into the foreach $themes loop.
global $wpdb; foreach ($themes as $theme) { $count = $wpdb->get_var( $wpdb->prepare( "SELECT count FROM $wpdb->term_taxonomy WHERE term_taxonomy_id = %d", $theme->term_taxonomy_id) ); /* Your code here to display the count ... */ }
While registering your custom taxonomy, you can link an update_count_callback function to it. This function will get called every time any term in your taxonomy gets a count update. This allows you to control what actually gets stored in the ‘count‘ column of your custom taxonomy terms.
$args = array( 'hierarchical' => false, 'update_count_callback' => 'test_taxonomy_count', 'label' => __('Theme'), 'query_var' => 'theme', 'rewrite' => array( 'slug' => 'theme' ) ) register_taxonomy( 'theme', 'post', $args); // This test count function just does the default WordPress operations function test_taxonomy_count($terms) { global $wpdb; $terms = array_map('intval', $terms); foreach ( (array) $terms as $term) { $count = $wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM $wpdb->term_relationships WHERE term_taxonomy_id = %d", $term) ); $wpdb->update( $wpdb->term_taxonomy, compact( 'count' ), array( 'term_taxonomy_id' => $term ) ); } }
5. All Done!
You can use the same code to style your custom taxonomy input panels for pages and links. Just change the ‘post‘ attribute to ‘page‘ or ‘link‘ when calling add_meta_box and use the ‘save_page‘, ‘edit_link‘, and ‘add_link‘ hooks instead of ‘save_post‘.
You can also add new fields to your WordPress blog categories using a similar system.
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Me again. Okay, so, I thought I was in the clear with that solution, but, alas, no bueno again. Turns out that using the code for the custom dropdowns is doing something wonky with the post counts in the taxonomy. When I clear out all taxonomy terms etc., fire up this code in functions file and go to admin, all looks good, 0 posts for term, but, when I add a term to a post, save and then go to the taxonomy menu, it says that there are 2 posts under that term when there is only one. When I then delete the term, it says there is 1, when there is now 0. If I remove the custom styling/saving from functions file and repeat process using default meta box, the count is correct, 0,1,0. Any clues on this one?
Thanks for uncovering this bug.
The reason why count is incremented twice is because a taxonomy relationship gets saved for the post and another gets saved for the post revision.
To fix this count problem, do a post_type check in your save_taxonomy_data function, e.g.
I will update the article tomorrow. Now I am off to bed.
I’m really struggling to figure out where to add in the show_option_none in this code so that there is an option to remove the taxonomy from a post if assigned in error. I see that it is available in the image example of your code, so, perhaps you could enlighten us?? Would be greatly appreciated. I believe your example here is the only one on the internet at present discussing how to customize the administrative inputs for custom taxonomies, so, thank you very much for that. I would love to see this elaborated on even more by those in the know. I’ve been wrecking my brain trying to work out how to provide multiple input options on a site I’m currently developing. I know things are about to change considerably in WP3.0, so, I want to be sure that the methods that I am using initially will be easily converted to take advantage of the new core functions once they are implemented.
Hello Angelia,
One way to do it is to add an additional “None” option to the drop down menu, [I have added it to the article above] e.g.
This will set the theme taxonomy value to NULL later on in the save_taxonomy_data function – i.e., it will remove the taxonomy term from the post.
Let me know if you run into more problems.
Thanks so much for the help Shibashake! I’ve just about been driving myself batty with all of this
I have a client site that I’m building currently, and the main thing that they provide is lesson plans for teachers. My goal is to construct a backend admin that makes it easy for teachers to create the plans in the post editor ( taxonomy non-hierarchical modules ( dropdown ) for grade level, subject etc., custom taxonomy heirarchical for a gigantic ( dropdown ) listing of applicable state standards ), custom taxonomy default selection for general things like materials and the default post tags for other searchable descriptions … you get the point. Of course, then I have to have all of those same modules provide for in-depth searchability of the plans for the front end user. The new taxonomy, custom post types, and admin hooks are absolutely perfect for implementing all of this, but, my goodness, not only is there very little info out there at the moment, I’ve been watching the trac to see how things are coming along, and just about everything that I need to custom code to make this happen, is going to be implemented in 3.0. I’m pulling my hair out to work out how I should implement this stuff now, without having to redo everything in a month from now. I’ve scoured the available plugins ( simple taxonomies, custom taxonomies and gdtaxonomy tools ) in an attempt to put something custom together for my client to be able to use now, but, they all fall short in one way or another. Custom Taxonomies creates its own table, and I experienced some duplicate counts with it, not to mention there is a bug with not being able to deselect a selected term in the custom checkbox metabox. Simple taxonomies is really really simple, providing a nice start, but, doesn’t take into account hierarchical, or custom post type. I tried implementing them in there myself, but, no bueno. GD tools is mostly fluff, and the one feature that I was interested ( deletion ) doesn’t work. I checked the database twice, and the terms were still there. I’ve never written my own plugin from scratch, I mostly just do customizations of existing code ( self-taught … what can I say ), so I’m not really confident yet in my ability to put a beast like that together properly myself, especially after looking through the trac at all of the customizations that are having to be made on so many levels of core files just to implement these big changes.
It seems that in the trac, they are extending Walker to deal with dropdowns for hierarchical terms.
I’m rambling. My conclusion is to 1. remove any plugin attempts ( my custom ones or otherwise ) for now, 2. stick to the basics ( with your style inclusions ) 3. keep it all in the functions file and 4. hold off on implementing the hierarchical taxonomies until the 3.0 release. Then I’ll just hold my breath that along with the 3.0 release comes a taxonomy column in edit.php, singular and plural terms, easy styling of meta boxes, and the ability to transition what I’m doing in my functions file, to the core without screwing anything up in the database, ie unregister_taxonomy. Ha! Wish me luck. Should be fun explaining all of this to my client … always is.
Thanks Leo – that is very good advice. I have added it to the article
Not at all. Also thank you for teaching me with the custom taxonomies.
Hello, I got error with your_styling_function
Says “Warning: strcmp() expects parameter 2 to be string”.
I just copy and paste your code, nothing modified.
Thanks for pointing that out Leo. The strcmp command should actually read -
There should be a ‘->name’ after $names[0]. Please let me know if you run into any more problems.
Thank you for quick reply. It works!
I think it’s better to use remove_meta_box to remove the original input taxonomy box, rather than register it to “shiba_post”. In this way the “Theme” tab will still appear in the admin menu, as a submenu under “Posts”, this lets other webmasters easily add more taxonomies.
Thanks again.
Sorry, I mean add more terms in that taxonomy, actually.
what an amazing site .Ilove it alot .
with my hearty wishes
bye
Glad you enjoyed it and thanks for dropping by
Hope to see you again.
[...] [...]
Hello Giraldi,
Haven’t done anything like that myself … the best way to go would depend somewhat on the complexity of your hierarchy. If it is free-form like WP categories then it is probably easiest to look at the WP source and adapt the existing code to your own needs.
The wp_dropdown_categories function is in the wp-includes/category-template.php file. I looked at it briefly, and it definitely looks adaptable.
The function itself is not very large, and it only uses one core object – Walker_CategoryDropdown which can be found in wp-includes/classes.php.
Instead of doing -
Get you own list of taxonomy objects instead. Then you will also need to play around with the Walker_CategoryDropdown object in terms of what attributes you want to display.
Thanks for the reply, ShibaShake! However, I had found the solution from this link: http://wphacks.com/how-to-display-wordpress-tags-dropdown-menu/, with some modification of course.
Tx for the great tute, ShibaShake! Been looking for this.
Just wondering, though.. Do you know how to create, with custom taxonomies, something similar to wp_dropdown_categories, that is, I need to have it show the post count and also be in a dropdown menu in the home page?
Tx agian for the tute! Cheers!
Hi MacBoy,
Glad you enjoyed the tutorial
I am actually not affiliated with Justin. I do enjoy his articles, so I link to them when I write about related topics.
Hey there ShibaShake,
This is an excellent tutorial. I’m glad that I’ve found a teammate of Justin Tadlock’s!
You have a terrific talent in explaining things, keep it up!
Oh btw – also look into using child themes so that you can easily keep all your changes across theme updates.
I added the lines of code from the first 2 sub-chapters, to the default WP theme, and i got: “Warning: call_user_func(your_styling_function) [function.call-user-func]: First argument is expected to be a valid callback in /Library/WebServer/Documents/testwp5/wp-admin/includes/template.php on line 2936″
screenshot here: http://img30.imageshack.us/img30/4889/shibaprintscreen.jpg
Ok – it is because you did not yet define a “your_styling_function”.
Just paste the your_styling_function example I gave above (the 3rd code snippet) into your functions.php file and the warning should go away.
It goes in the functions.php file – best in a child theme area.
the register_taxonomy line goes into your functions.php file as well. I just pasted that exact line in my functions.php, and it seemed to work fine, so I am not sure where your error is coming from.
Could you post some of your surrounding code? Might help in seeing what the issue is.
This tutorial answered a lot of questions in using WP Custom Taxonomies – as the codex is very shy on documentation and examples.
Problem I couldn’t use it.
From the beginning: To restyle the custom taxonomy input interface, you must use the add_meta_box command. – use it where?
Further on I get a Parse error: syntax error, unexpected ‘=’, expecting ‘)’ error, somewhere it seems because of this line
register_taxonomy( 'theme', 'post', array( 'hierarchical' => false, 'label' => __('Theme'), 'query_var' => 'theme', 'rewrite' => array( 'slug' => 'theme' ) ) );