WordPress Functions

WordPress: register_post_meta Funciton

26 October 2023

Are you familiar with the popular saying “every piece of information matters”? As a web developer, this plays out on the regular, especially when dealing with posts or pages on a website. For instance, you may need a unique identifier for particular blog posts or pages on your website, perhaps to provide users with personalized services or strategically position promotions. This is where our function ‘register_post_meta’ steps into the limelight.

It’s like a reliable assistant that steps in and says, “Hey, let me remember that for you”. It commits to memory these vital pieces of information (meta keys) relevant to specific or all types of post, and brings them forth on demand. Not just that, it goes further to meticulously present a comprehensive description of these meta keys. The underlying potential of ‘register_post_meta’ in creating a robust structure for your website is indeed limitless. Toss in arguments defining your preferred types and style, and it caters specifically to your needs. Talk about exquisite customization!

Syntax

register_post_meta( $post_type, $meta_key, $args )
Parameters
  • $post_type (string): The post type to register a meta key for. Pass an empty string to register the meta key across all existing post types.
  • $meta_key (string): The meta key to register.
  • $args (array): Data used to describe the meta key when registered. See register_meta() for a list of supported arguments.
Return Value
  • (bool) – Returns true if the meta key was successfully registered, and false if not.

How it works

<?php
/**
* Registers a meta key for posts.
*
* @since 4.9.8
*
* @param string $post_type Post type to register a meta key for. Pass an empty string
* to register the meta key across all existing post types.
* @param string $meta_key The meta key to register.
* @param array $args Data used to describe the meta key when registered. See
* {@see register_meta()} for a list of supported arguments.
* @return bool True if the meta key was successfully registered, false if not.
*/
function register_post_meta( $post_type, $meta_key, array $args ) {
$args['object_subtype'] = $post_type;
return register_meta( 'post', $meta_key, $args );
}

The register_post_meta() function is used to register a custom meta key for posts. A meta key is essentially a custom field that can be associated with posts. When calling this function, you need to provide the following parameters:

  • $post_type: A string representing the post type you want to register the meta key for. You can pass an empty string ” to register the meta key across all existing post types.
  • $meta_key: The name or identifier of the custom meta key you want to register.
  • $args: An array containing additional data and settings related to the meta key registration. This array should include elements following the specifications described in register_meta(), which provides a list of supported arguments.

Inside the function, we modify the $args array by adding an additional element called ‘object_subtype’, which is equal to the value of $post_type. This tells WordPress that this particular meta key should only be registered for posts of a specific post type.

Finally, we call register_meta(), passing ‘post’ as the object type and using the provided $meta_key and modified $args. This function is responsible for actually registering the meta key in the WordPress database. If successful, we return the result of register_meta() to indicate that the registration was completed.

Usage

Example 1: Registering a Meta Key for Posts

<?php
// Register a meta key for all post types
$args = [
"single" => true,
"type" => "string",
"show_in_rest" => true,
"auth_callback" => "my_auth_callback",
];
register_post_meta("", "my_meta_key", $args);

In this example, we register a meta key called “my_meta_key” for all existing post types. We define the arguments for the meta key, including its type, whether it should be shown in the REST API, and an authentication callback function. This function ensures that only authorized users can access or modify the meta key.

Example 2: Registering Meta Key for Custom Post Type

// Register a meta key for a custom post type called "product"
add_action("init", "register_product_meta");
function register_product_meta()
{
$args = [
"single" => true,
"type" => "integer",
"show_in_rest" => true,
];
register_post_meta("product", "product_price", $args);
}
// Update the product price meta data
add_action(
"woocommerce_process_product_meta",
"update_product_price_meta",
10,
2
);
function update_product_price_meta($post_id, $post)
{
if (isset($_POST["product_price"])) {
update_post_meta(
$post_id,
"product_price",
sanitize_text_field($_POST["product_price"])
);
}
}

In this example, we register a new meta key called “product_price” specifically for a custom post type called “product”, which is used in an eCommerce website powered by WooCommerce. By using the register_post_meta() function hooked into the init action, we ensure that the meta key is registered when the website is initialized.

To update the product price meta data, we use another hook called woocommerce_process_product_meta. This hook fires when a product is saved or updated in the WooCommerce admin. Inside the callback function, we check if the $_POST variable contains the product price field and update its value using update_post_meta().

By registering and updating custom meta data for our custom post type, we can store additional information such as pricing details for our products.

Example 3: Registering Custom Meta Key with Custom Permissions

<?php
// Register a meta key with custom permission requirements
$args = [
"single" => true,
"type" => "string",
"show_in_rest" => true,
"meta_capability" => "edit_custom_fields",
];
register_post_meta("", "my_custom_key", $args);

In this example, we register a meta key called “my_custom_key” for all existing post types. We customize the permissions required to edit this meta key by setting the meta_capability argument to ‘edit_custom_fields’. This means that users must have the ‘edit_custom_fields’ capability in order to modify this specific meta key’s value.

By leveraging this functionality, you can create fine-grained control over who can access and modify certain meta keys on your posts. This can be useful when working with sensitive or restricted data that should only be editable by certain user roles or capabilities.

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