WordPress Post Meta ideas

gistfile1.php

<?php

/**
 * Post Meta Box view/controller class.
 *
 * Extends from a form object base class.
 *
 * Creates a meta box. Fields can be related to the meta box, but
 * all business logic lives within the field object.
 */
class WP_Post_Meta_Box extends WP_Form_Object {

	function __construct() {
		// Register object-specific UI
		add_action( 'add_meta_boxes', array( $this, 'add_meta_box' ) );

		// Register data saving handler.
		add_action( 'save_post', array( $this, 'save' ), 10, 2 );
	}

	/**
	 * Register a meta box.
	 */
	function add_meta_box() {}

	/**
	 * Output the contents of the meta box.
	 */
	function metabox_callback() {
		$this->render_form();
	}

	/**
	 * Render input elements for all related fields.
	 */
	function render_form() {
		foreach ( $this->get_fields() as $field ) {
			$field->render_input_element();
		}
	}

	/**
	 * Save data or each field according to the object's data model.
	 */
	function save( $post_id, $post ) {
		foreach ( $this->get_fields() as $field ) {
			$this->save_field( $field );
		}
	}

	/**
	 * Save method specific to the object type.
	 */
	function save_field( $field ) {
		global $post;
		update_post_meta( $post->ID, $field->slug, $this->get_field_value( $field ), true );
	}

	/**
	 * Retrieve a user-submitted value for a field.
	 *
	 * This may need to call the field object/class, depending how
	 * $_POST variable names are built.
	 */
	function get_field_value( $field ) {}

	/**
	 * Get field objects related to this form object.
	 */
	function get_fields() {}
}

add_action( 'init', 'register_custom_fields' );

function register_custom_fields() {
	register_field( array(
		'objects' => array( 'post', 'page' ),
		'slug' => 'background_color',
		'type' => 'color', // Relates to a pre-defined class.
		'auth_callback' => 'callback_function',
		'sanitization_callback' => 'sanitization_function',
	) );

}

/**
 * Field registration.
 *
 * Abstracted from the UI view class, so that the field's business logic
 * and data describing it can be accessed independently.
 *
 * Data about fields is stored in a nested array.
 */
function register_field( $args ) {
	global $object_fields;

	// Parse args with defaults...

	// Sanitize data...

	if ( is_array( $args['objects'] ) {
		foreach ( $objects as $object_type ) {
			$object_fields[$object_type][] = array(
				// Add data...
			);
			// register_meta etc depending on object type...
		}
	}
}

add_action( 'init', 'register_form_containers' );
/**
 * Register form contianer.
 */
function register_form_containers() {
	// Insantiate a container.
	$container = new WP_Post_Meta_Box();

	// Relate a registered field to the container.
	$container->add_field( array( 'slug' => 'background_color' ) );
}

/**
 * Text input class. Essentially, a view.
 *
 * Provides form element HTML markup, script enqueueing, etc.
 *
 * Relates to a field type.
 */
class Input_Text extends Input {}

Looks good for a first pass. Here are my concerns after a quick read:

• WP_Post_Meta_Box - Do we want to couple a post form to a meta box?
• Render - Do we want to use that term when little else in WordPress uses render()? Why not the_form()?
• 'objects' - Shouldn't this be be 'post_types?' Or shouldn't they be qualified, i.e. 'post/post', 'post/page', 'user', etc.
• Callbacks - Do we want use callbacks, or use a declarative approach combine with filters for customization?
• $object_fields - Do we want to use globals vs. a private property as WP_Theme, WP_Screen, WP_Admin_Bar etc. are doing?
• register_field() - Do we want it to process $args immediately, or store and continue w/later fixup after an 'init' hook?
• WP_Form_Object - What does it look like?
• _Object prefix - Do we need that? It's not used anywhere else in WordPress.
• 'register_form_containers' - How/where does it register it's "containers?" Why is form_ an adjective for container; are WP_Post_Meta_Boxes not more specific forms? Why not register_form() in 'init'?
• Input - Do we want to use the name Input for base class since HTML data entry fields include <input>, <select>, <textarea> and more?

I think we agree on these, this will definitely be evolving and naming/args haven't been nailed down yet.

Looking great. I understand this is pseudo-code, but agree with @mikeschinkel about not tying down metaboxes/forms to a post object.

The use of globals here is unwarranted, and will lead to bugs, e.g.:

https://gist.github.com/ericandrewlewis/8290246#file-gistfile1-php-L56

What if I pass in a post ID to save_post that isn't the ID of $post ? What if for whatever reason $post is not defined? In this case there is no reason at all for the post_id not to be an argument, it's available in the calling method save_post.