add_post_meta, get_post_meta (ok)

https://developer.wordpress.org/reference/functions/add_post_meta/

add_post_meta

C:\xampp\htdocs\wordpress\wp-content\themes\twentytwentyone\index.php

add_post_meta( 1, 'lionel____ticket', 'pia', true );

get_post_meta

echo 'aaaaa1';
echo get_post_meta(1,'lionel____ticket',true); 
echo 'aaaaa2';

Một ví dụ thực hiện trên app những bài viết đã xem :)

public function get_item( $request ) {
		$post = $this->get_post( $request['id'] );
		if ( is_wp_error( $post ) ) {
			return $post;
		}

		$data     = $this->prepare_item_for_response( $post, $request );
		$response = rest_ensure_response( $data );

		if ( is_post_type_viewable( get_post_type_object( $post->post_type ) ) ) {
			$response->link_header( 'alternate', get_permalink( $post->ID ), array( 'type' => 'text/html' ) );
		}
		$wp_request_headers = array(
    	'Authorization' => 'Basic ' . base64_encode( 'wordpress:wordpress' )
		);
		$wp_request_url = 'http://app.yp.vn/wp-json/wp/v2/posts/'.$request['id'];
		$wp_delete_post_response = wp_remote_request(
		    $wp_request_url,
		    array(
	        'method'    => 'GET',
	        'headers'   => $wp_request_headers
		    )
		);
		wp_remote_retrieve_response_code( $wp_delete_post_response );
		wp_remote_retrieve_response_message( $wp_delete_post_response );
		// ==========
		if (is_user_logged_in()) {
			$current_user_id = get_current_user_id();
			$currentuseridpost = $current_user_id . '_' . $request['id'];
			add_post_meta( $request['id'], $currentuseridpost, 1, true );
		}
		return $response;
	}