get one post with specific conditions Ref: https://codex.wordpress.org/Class_Reference/WP_Query, http://codex.wordpress.org/Function_Reference/get_posts, https://developer.wordpress.org/reference/functions/get_post/

get-post-without-id.md

• WP supports only function get a post is get_post() function, but it just get information of post when you know post_id

$post = get_post($post_id);

• If you want to get post without post_id, must to use get_posts() function

$args = array(
  'posts_per_page' => 1, // required
   // ... your conditions, ex: 'post_type' => 'post', 'post_author' => 1
);
$posts = get_posts($args);
$post = null;
if ($posts)
  $post = $posts[0];

Ref:

• https://codex.wordpress.org/Class_Reference/WP_Query
• http://codex.wordpress.org/Function_Reference/get_posts
• https://developer.wordpress.org/reference/functions/get_post/