register_meta() is a tiny function, which lets you register a sanitization and authorization callback for post metaMeta Meta is a term that refers to the inside workings of a group. For us, this is the team that works on internal WordPress sites like WordCamp Central and Make WordPress., term meta, user meta or comment meta.

We’re going to expand the utility of this function to describe the data type of the field. This will be useful for the REST APIREST API The REST API is an acronym for the RESTful Application Program Interface (API) that uses HTTP requests to GET, PUT, POST and DELETE data. It is how the front end of an application (think “phone app” or “website”) can communicate with the data store (think “database” or “file system”) https://developer.wordpress.org/rest-api/. as well as the Fields APIAPI An API or Application Programming Interface is a software intermediary that allows programs to interact with each other and share data in limited, clearly defined ways..

This discussion has started in #35658, but I’d like to share the latest thoughts for general feedback.

Imagine a “movie” custom post typeCustom Post Type WordPress can hold and display many different types of content. A single item of such a content is generally called a post, although post is also a specific post type. Custom Post Types gives your site the ability to have templated posts, to simplify the concept. which has a “star-rating” post meta field, which should accept the value 1, 2, 3, 4 and 5. REST API clients like the iOSiOS The operating system used on iPhones and iPads. app would want to know this information, so they can offer appropriate UIUI User interface for their users. Ditto for the Fields API.

Here are some loose thoughts on what that API might look like.

Here is a post meta field for “mood” that accepts any string. The value would fit in a single row. There would only be one row per post, as it is not “repeatable.” Repeatable might be a default.

<?php 
register_meta( 'post', 'mood', array( 'schema' => array( 
		'type' => 'string',
		'repeatable' => false
	)
) );

Here is a field that consists of an array of URLs. The value would fit in a single row, perhaps in JSONJSON JSON, or JavaScript Object Notation, is a minimal, readable format for structuring data. It is used primarily to transmit data between a server and web application, as an alternative to XML. format, i.e. ['some.url/','some.other/url'], and is limited to one row per post.

<?php 
register_meta( 'post', 'related_content', array(
	'schema' => array( 
		'type' => 'array',
		'items' => array(
			'type' => 'url',
		),
		'repeatable' => false
	)
) );

Here is a field that consists of an album as it relates to an artist and includes a number of properties. The value would fit in a single row, and multiple rows can exist for a single artist.

<?php 
register_meta( 'post', 'album', array(
	'object_subtype' => 'artist',
	'schema' => array( 
		'type' => 'object',
		'properties' => array(
			'name' => array(
				'type' => 'string'
			),
			'cover' => array(
				'type' => 'wp-image'
			),
			'genre' => array(
				'type' => 'string',
				'options' => array( 'Rock', 'R&B', 'Shoegaze' ),
			),
			'release-date' => array(
				'type' => 'date'
			)
		)
		'repeatable' => true
	)
) );

What do you think?

#fields-api, #options-meta, #rest-api