The method of obtaining information for individual posts using REST API may be different depending on the permalink settings (note)

I am not giving a complete interpretation, but I am writing this as a memo because it seems like it when I actually tried it. ．． .

When obtaining information on individual posts via REST API, the endpoints differed as follows.

[If the permalink is ID (%post_id%)]

Home URL/wp-json/wp/v2/Post type (posts for posts)/ID

[If the permalink is other (character string)]

Home URL/wp-json/wp/v2/Post type (posts for posts)?slug=〇〇

And I found out that if the permalink is an ID, you have to use wp_remote_get(), and in other cases, you have to use file_get_contents() to get the information.

It took me quite a while to figure this out, but is this a WordPress specification or a bug? ．． I’m not sure.

By the way, the following is the code that was tested and completed. It roughly divides the permalink depending on whether it is a number or not, gets the ID of the eye-catching image, and outputs the value returned by the shortcode.

There are also differences in the variables when extracting with wp_remote_get() and file_get_contents(), so you may need to be careful.

function pwcn_rest_api_post_data_callback(){
/* Sample when the slug in a post is the post ID (%post_id) */
    //$home_url = '〇〇'; // Site URL
    //$post_type = 'posts'; // Post type
    //$slug = '△△'; // slug

/* Sample for character slug in post */
	$home_url = '〇〇';//Do not include the trailing "/"
	$post_type = 'posts';//Posts are "posts"
	$slug = '□□';//Do not include "/" before and after

/* Sample for custom post type + string slug */
	//$home_url = '〇〇';//Do not include the trailing
	//$post_type = '◇◇';//Posts are "posts"
	//$slug = '□□';//Do not include "/" before and after

//To prevent incorrect input, remove the "/" at the beginning of $slug and the end of $home_url.
    $slug = ltrim($slug, '/');
    $home_url = rtrim($home_url, '/');

if (ctype_digit($slug)) {// If the slug is only numbers
	$post_url = $home_url . '/wp-json/wp/v2/' . $post_type . '/' . $slug;
	$response = wp_remote_get($post_url); // Get data from REST API using wp_remote_get

	$body = wp_remote_retrieve_body($response); // Get response body
	$data = json_decode($body, true); // Decode JSON data

	if (isset($data['featured_media'])) {
		$image_id = $data['featured_media'];
	} else {
		$image_id =  'No images were found.';
	}

} else {//If the slug is not just numbers
	$post_url = $home_url . '/wp-json/wp/v2/' . $post_type . '?slug=' . $slug;
	
	//Get json data
		$json_data = file_get_contents($post_url);
		$decoded_data = json_decode($json_data, true);

// Get the ID of the featured image
	if (isset($decoded_data[0]['featured_media'])) {
		$image_id = $decoded_data[0]['featured_media'];
	}else{
		$image_id = 'Image not found';
	}
}
	return $image_id;
}

function view_data(){
    $image_id = pwcn_rest_api_post_data_callback();
        return $image_id;
}
add_shortcode('test-post-view','view_data');

If you actually have a site with an ID permalink structure and another site, you might be able to say “I see” if you try it.

Please note that this page is a verification result as of WordPress 6.5, and the behavior may be different in other versions, and the environment may be affected. I would be happy if I could share my opinion with someone who has a personal solution.

but. ．． If this were the specification, it would be quite confusing. ．． ．． .