Custom taxonomies in Wordpress

Introduction

Custom taxonomies help you organize content in WordPress beyond default categories and tags. They let you group posts or items in ways that fit your site.

You want to group products by brand on an online store.

You need to organize blog posts by topic and difficulty level.

You want to classify events by location or type.

You want to add custom filters for recipes by cuisine or cooking time.

Syntax

Wordpress

register_taxonomy( string $taxonomy, array|string $object_type, array|string $args = array() )

Use register_taxonomy inside a function hooked to init action.

The $taxonomy is the name of your custom taxonomy (like 'genre').

Examples

This creates a simple taxonomy called 'genre' for blog posts.

Wordpress

function create_genre_taxonomy() {
  register_taxonomy('genre', 'post');
}
add_action('init', 'create_genre_taxonomy');

This creates a hierarchical taxonomy 'brand' for products, like categories.

Wordpress

function create_product_brand_taxonomy() {
  register_taxonomy('brand', 'product', [
    'label' => 'Brands',
    'hierarchical' => true
  ]);
}
add_action('init', 'create_product_brand_taxonomy');

This creates a non-hierarchical taxonomy 'event_type' for events and posts, like tags.

Wordpress

function create_event_type_taxonomy() {
  register_taxonomy('event_type', ['event', 'post'], [
    'label' => 'Event Types',
    'hierarchical' => false
  ]);
}
add_action('init', 'create_event_type_taxonomy');

Sample Program

This code creates a custom taxonomy called 'genre' for a custom post type 'movie'. It is hierarchical, so it works like categories. It also shows in the admin area for easy use.

Wordpress

<?php
function create_movie_genre_taxonomy() {
  $args = [
    'label' => 'Genres',
    'public' => true,
    'hierarchical' => true,
    'show_ui' => true,
    'show_admin_column' => true
  ];
  register_taxonomy('genre', 'movie', $args);
}
add_action('init', 'create_movie_genre_taxonomy');

// This code adds a 'genre' taxonomy for 'movie' post type.
?>

Important Notes

Always hook your taxonomy registration to the init action to ensure WordPress is ready.

Hierarchical taxonomies behave like categories (can have parent-child), non-hierarchical like tags (flat list).

Use descriptive labels to make your taxonomy clear in the admin dashboard.

Summary

Custom taxonomies help organize content in ways that fit your site.

Use register_taxonomy inside an init hook to create them.

Choose hierarchical or non-hierarchical depending on how you want to group items.

Practice

1. What is the main purpose of creating a custom taxonomy in WordPress?

easy

A. To increase website loading speed

B. To change the website's theme colors

C. To add new user roles

D. To organize content in a way that fits your website's needs

Solution

1. Step 1: Understand what taxonomy means in WordPress

   Taxonomies group content like categories or tags to organize posts.

2. Step 2: Identify the purpose of custom taxonomies

   Custom taxonomies let you create your own groups to better fit your content.

3. Final Answer:

   To organize content in a way that fits your website's needs -> Option D

4. Quick Check:

   Custom taxonomy = organize content [OK]

Hint: Custom taxonomies organize content, not change design or speed [OK]

Common Mistakes:

• Confusing taxonomies with themes or plugins
• Thinking taxonomies affect site speed
• Mixing taxonomies with user roles

2. Which of the following is the correct way to register a custom taxonomy called genre for posts in WordPress?

easy

A. register_taxonomy('genre', 'post', array('hierarchical' => true));

B. register_taxonomy('genre', 'posts', array('hierarchical' => true));

C. register_taxonomy('genre', array('post'), 'hierarchical' => true);

D. register_taxonomy('genre', 'post', 'hierarchical' => true);

Solution

1. Step 1: Check the function signature of register_taxonomy()

   The function requires taxonomy name, object type(s) as string or array, and an array of arguments.

2. Step 2: Verify correct parameter types and syntax

   register_taxonomy('genre', 'post', array('hierarchical' => true)); uses 'post' as string and an array for arguments correctly.

3. Final Answer:

   register_taxonomy('genre', 'post', array('hierarchical' => true)); -> Option A

4. Quick Check:

   Correct syntax uses array for args and string for post type [OK]

Hint: Use array() for args and string or array for post types [OK]

Common Mistakes:

• Using plural 'posts' instead of 'post'
• Passing arguments outside an array
• Wrong parameter order

3. Given this code snippet:

register_taxonomy('genre', 'post', array('hierarchical' => true));
$terms = get_terms(array('taxonomy' => 'genre', 'hide_empty' => false));
foreach ($terms as $term) {
  echo $term->name . ', ';
}

What will this code output if there are two terms 'Fiction' and 'Non-Fiction' assigned to posts?

medium

A. genre, Fiction, Non-Fiction

B. Fiction, Non-Fiction,

C. Array

D. Error: Undefined variable

Solution

1. Step 1: Understand get_terms() usage

   get_terms() fetches terms of the taxonomy 'genre' including empty ones due to 'hide_empty' => false.

2. Step 2: Loop through terms and print their names

   The foreach loop prints each term's name followed by a comma and space.

3. Final Answer:

   Fiction, Non-Fiction, -> Option B

4. Quick Check:

   Loop prints term names separated by commas [OK]

Hint: get_terms returns term objects; loop prints their names [OK]

Common Mistakes:

• Expecting taxonomy name instead of term names
• Confusing array output with string
• Not setting 'hide_empty' causing missing terms

4. What is wrong with this code snippet for registering a custom taxonomy?

register_taxonomy('genre', 'post', 'hierarchical' => true);

medium

A. The post type should be an array, not a string

B. The taxonomy name must be plural

C. The third argument should be an array, not a key-value pair directly

D. The function name is incorrect

Solution

1. Step 1: Check the function parameters

   register_taxonomy() expects the third argument as an array of arguments.

2. Step 2: Identify the error in argument format

   The code passes 'hierarchical' => true directly, not inside an array, causing syntax error.

3. Final Answer:

   The third argument should be an array, not a key-value pair directly -> Option C

4. Quick Check:

   Args must be in array() [OK]

Hint: Always wrap arguments in array() for register_taxonomy [OK]

Common Mistakes:

• Passing arguments without array()
• Using plural taxonomy names incorrectly
• Wrong function name like register_taxonomies

5. You want to create a custom taxonomy called location that behaves like tags (non-hierarchical) and attach it to both post and event post types. Which code snippet correctly achieves this?

hard

A. register_taxonomy('location', array('post', 'event'), array('hierarchical' => false));

B. register_taxonomy('location', 'post', array('hierarchical' => false)); register_taxonomy('location', 'event', array('hierarchical' => false));

C. register_taxonomy('location', array('post', 'event'), array('hierarchical' => true));

D. register_taxonomy('location', array('post', 'event'), array('hierarchical' => true, 'tags' => true));

Solution

1. Step 1: Understand hierarchical argument for tags

   Tags are non-hierarchical, so 'hierarchical' must be false.

2. Step 2: Attach taxonomy to multiple post types

   Pass an array of post types ['post', 'event'] as second argument.

3. Step 3: Check options for correct syntax and behavior

   register_taxonomy('location', array('post', 'event'), array('hierarchical' => false)); correctly sets 'hierarchical' => false and attaches to both post types in one call.

4. Final Answer:

   register_taxonomy('location', array('post', 'event'), array('hierarchical' => false)); -> Option A

5. Quick Check:

   Non-hierarchical + multiple post types = register_taxonomy('location', array('post', 'event'), array('hierarchical' => false)); [OK]

Hint: Use array for post types and set hierarchical false for tags [OK]

Common Mistakes:

• Setting hierarchical true for tags
• Calling register_taxonomy twice unnecessarily
• Passing post types as string instead of array