Metadata

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• Overview
• Function Reference
• Database Requirements
• Default Meta Tables
• Meta Table Structure
• Source File
• Related

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Overview

The Metadata API is a simple and standarized way for retrieving and manipulating metadata of various WordPress object types.

Metadata for an object is a represented by a simple key-value pair.

Objects may contain multiple metadata entries that share the same key and differ only in their value.

Function Reference

Add/Delete Metadata:

• add_metadata()
• delete_metadata()

Get/Update Metadata:

• get_metadata()
• update_metadata()

Database Requirements

This function assumes that a dedicated MySQL table exists for the $meta_type you specify. Some desired $meta_types do not come with pre-installed WordPress tables, and so they must be created manually.

Default Meta Tables

Assuming a prefix of wp_, WordPress’s included meta tables are:

• wp_commentmeta: Metadata for specific comments.
• wp_postmeta: Metadata for pages, posts, and all other post types.
• wp_usermeta: Metadata for users.

Meta Table Structure

To store data for meta types not included in the above table list, a new table needs to be created. All meta tables require four columns.

• meta_id – BIGINT(20): unsigned, auto_increment, not null, primary key.
• object_id – BIGINT(20): unsigned, not null.
  Replace object with the singular name of the content type being used.
  For instance, this column might be named post_id or term_id.
  Although this column is used like a foreign key, it should not be defined as one.
• meta_key – VARCHAR(255): The key of your custom meta data.
• meta_value – LONGTEXT: The value of your custom meta data.

Source File

Metadata API is located in wp-includes/meta.php.

Related

Metadata API: add_metadata(), get_metadata(), update_metadata(), delete_metadata().