WordPress Metadata API

The Metadata API in WordPress is a set of functions that allow developers to store, retrieve, update, and delete metadata for posts, users, comments, and terms. Metadata provides a flexible way to attach extra data to existing WordPress objects, beyond standard fields.

Types of Metadata

WordPress supports metadata for four core object types:

• Post Meta (wp_postmeta)
• User Meta (wp_usermeta)
• Comment Meta (wp_commentmeta)
• Term Meta (wp_termmeta)

Each type of metadata is stored in a dedicated database table.

Core Functions

Function	Description
add_metadata()	Add new metadata to an object
get_metadata()	Retrieve existing metadata
update_metadata()	Update existing metadata
delete_metadata()	Remove metadata from an object

For convenience, these functions have wrapper functions like add_post_meta(), get_user_meta(), etc.

Example (Post Meta):

// Add custom field (meta)
add_post_meta( $post_id, 'price', '20.00' );

// Retrieve custom field
$price = get_post_meta( $post_id, 'price', true );

// Update custom field
update_post_meta( $post_id, 'price', '25.00' );

// Delete custom field
delete_post_meta( $post_id, 'price' );

When to Use Metadata

• Custom fields (like Advanced Custom Fields – ACF)
• Additional user profile data
• Custom settings for posts or terms
• Extra information for comments or reviews
• Extending core WordPress objects

How is Metadata Stored?

• Stored as key-value pairs (similar to Options API)
• Serialized automatically if storing arrays or objects
• Easily queryable via WP_Query or WP_User_Query

Best Practices

• Use descriptive, prefixed meta keys (myplugin_price instead of just price)
• Avoid excessive queries by caching metadata
• Limit the use of serialized data for performance reasons