Association field with custom values

association-custom-values.php

<?php

# Our available options
function crb_test_options() {
	return array(
		123 => array(
			'id' => 123, // ID of the entry, value that is saved in the DB, should be the same as the array key.
			'title' => 'Test Title', // title of the item, used for displaying the item in the admin
			'type' => 'test', // type of the item, used for identifying this type of item
			'subtype' => 'test item', // subtype of the item, in this solution it will be used only for presentation purposes
			'label' => 'test item', // label of the item, used for displaying the item in the admin
			'is_trashed' => false, // trashed status
		),
		456 => array(
			'id' => 456,
			'title' => 'Test Title',
			'type' => 'test',
			'subtype' => 'test item',
			'label' => 'test item',
			'is_trashed' => false,
		),
	);
}

# Add the custom options to that custom field
add_filter( 'carbon_relationship_options', 'crb_carbon_relationship_options', 10, 2 );
function crb_carbon_relationship_options( $options, $field_name ) {
	# Targeting only the necessary association field
	if ( $field_name === '_crb_assoc_test' ) {
		$options = crb_test_options();
	}

	return $options;
}

# Make sure that the association field knows how to retrieve the item title
add_filter( 'carbon_relationship_title', 'crb_carbon_relationship_title', 10, 5);
function crb_carbon_relationship_title( $title, $field_name, $id, $type, $subtype ) {
	# Targeting only the necessary association field
	if ( $field_name !== '_crb_assoc_test' ) {
		return $title;
	}

	$options = crb_test_options();
	$title = $options[ $id ][ 'title' ];
	return $title;
}

# Make sure that the association field knows how to retrieve the item label
add_filter( 'carbon_relationship_label', 'crb_carbon_relationship_label', 10, 5);
function crb_carbon_relationship_label( $label, $field_name, $id, $type, $subtype ) {
	# Targeting only the necessary association field
	if ( $field_name !== '_crb_assoc_test' ) {
		return $label;
	}

	return 'Test Item';
}

# Define the carbon container and the association field
Carbon_Container::factory( 'custom_fields', __( 'Custom Data', 'crb' ) )
	->show_on_post_type( 'page' )
	->add_fields(array(
		Carbon_Field::factory( 'association', 'crb_assoc_test' )
			->set_types( array(
			) ),
	));