WordPress snippets I might need again at some point

Polylang language in REST API

Polylang is a popular multilinguality plugin for WordPress. The pro version of it also provides some additional REST API endpoints. So in the regular version a request like the following will return all posts and just ignore the lang parameter:

GET /wp/v2/posts?lang=en

Still, you can filter by language by adding a ustom REST field through your themes functions.php:

function my_theme_filter_rest_post_query( $args, $request ) {
	$lang_parameter = $request->get_param('lang');
 
	if ( isset( $lang_parameter ) ) {
		$args['lang'] = $lang_parameter; // https://polylang.pro/doc/developpers-how-to/#query
	}
 
	return $args;
}
add_filter( 'rest_post_query', 'my_theme_filter_rest_post_query', 10, 2 );
add_filter( 'rest_page_query', 'my_theme_filter_rest_post_query', 10, 2 );
//add_filter( 'rest_{my_custom_posttype}_query', 'my_theme_filter_rest_post_query', 10, 2 ); // Custom posttype
 
add_action( 'rest_api_init', function () {
 
	register_rest_field( 'post', 'language', my_theme_register_postlanguage_function() );
	register_rest_field( 'page', 'language', my_theme_register_postlanguage_function() );
	//register_rest_field( '{my_custom_posttype}', 'language', my_theme_register_postlanguage_function() ); // Optional: Custom posttype
 
});
 
function my_theme_register_postlanguage_function() {
	return array(
		'methods'         => 'GET',
		'get_callback'    => 'my_theme_get_postlanguage_function',
		'schema'          => null,
	);
}
 
function my_theme_get_postlanguage_function( $data ) {
	$post_id = $data['id'];
	return ( function_exists( 'pll_get_post_language' ) ? pll_get_post_language( $post_id ) : null );
}

This code was originally written by them-es.

ACF fields in REST API

ACF is another popular WordPress plugin for adding custom fields to WP posts and pages (you can add a short summary, social links etc. etc. for example). These fields are also not included in the standard WP REST API, even if in the ACF settings you activate Show In REST API in the respective field group (even though according to the ACF documentation it should).

Again, you can add a simple snippet to the functions.php file in order to retrieve the acf fields, too:

function acf_to_rest_api($response, $post, $request) {
    if (function_exists('get_fields') && isset($post->id)) {
        $response->data['acf'] = get_fields($post->id);
    }
    return $response;
}
add_filter('rest_prepare_post', 'acf_to_rest_api', 10, 3);

(This code was taken from here.)

Try GET /wp/v2/posts and every post should now have your custom fields from AC included.

Redirect frontend to elsewhere

When using a headless WordPress setup, I ran into a situation where I wanted to have the WordPress admin section be served on www.example.com/wp-admin, but visitors should not be allowed to go see any WordPress frontend under www.example.com. Instead they should be redirected to the new frontend I host under www.elpmaxe.com. In order to do that I built a super minimal theme which only redirects frontend traffic and does nothing else (for which I used this solution):

under themes/create a folder called redirect
add a style.css and an index.php to it

style.css should look like this:

/*
   Theme Name: Redirect
   Description: Redirects the front end to elpmaxe.com
*/

style.css should look like this:

<?php
     header( "Location: https://www.elpmaxe.com" );
?>

activate the theme in the admin UI.

Add CORS header to MyCalender plugin

MyCalendar is a WordPress plugin for creating calendars. Under ‘Advanced Settings’ you can activate exposing its API, which will let you fetch events from the calendar like that: GET https://example.com?to=2024-06-25&from=2024-05-26&mc-api=json. However, when working in a local development environment you might run into CORS issues, so you should

But you can add to following lines to the top of some file in your theme or plugins in order to allow fetching from everywhere:

function add_cors_http_header(){
    header("Access-Control-Allow-Origin: *");
}
add_action('init','add_cors_http_header');

I added it to /httpdocs/wp-content/plugins/my-calendar/my-calender.php hoping that the CORS header will be scoped only to the MyCalendar routes, but I don’t think that’s the case. It’s also not the best idea to add custom code in plugins files instead of themes files, because the code might get overwritten when updating the respective plugin.

Moving wordpress from one server to another without plugins

Step 0

Step 1

zip the public folder (e.g. `/var/www/wordpress) and download

Step 2

export the database via phpmyadmin

Step 3

create a database on your new server and import the backup
change the database credentials in wp-config.php
use wp-cli in order to seacrch-and-replace all links in your database with wp search-replace '://olddomain.com' '://new domain.com' --all-tables

WordPress quirks

Posting a couple of quirks in WordPress, that I’m likely to forget how to deal with.

wp-block-post-template-inline-css

When I migrated a WordPress blog from my local dev environment to a webhosting, certain CSS files were not included in the <head>, for example wp-block-post-template-inline-css. I couldn’t find out what was causing this, but in the WordPress support forum someone had the same issue and the solution was to delete the _transient_wp_core_block_css_files entry from the wp_options table in your WordPress database.

Get featured image of a blog post from REST API

If you want to fetch the featured image of a blog post, you will need to include _embed as a search param in your REST call: curl https://example.com/wp-json/wp/v2/posts?_embed. You will then be able to find the image nested in the response object: response_object._embedded['wp:featuredmedia']['0'].source_url. By adding the following to your functions.php you will get a fimg_url field directly on response_object:

add_action('rest_api_init', 'register_rest_images' );
function register_rest_images(){
    register_rest_field( array('post'),
        'fimg_url',
        array(
            'get_callback'    => 'get_rest_featured_image',
            'update_callback' => null,
            'schema'          => null,
        )
    );
}
function get_rest_featured_image( $object, $field_name, $request ) {
    if( $object['featured_media'] ){
        $img = wp_get_attachment_image_src( $object['featured_media'], 'app-thumb' );
        return $img[0];
    }
    return false;
}

(source)

Scripts are not loading

If you’re building a custom theme and WordPress is not loading all the default scripts it is usually loading (e.g. wp-mediaelement/MediaElement.js, which are necessary vor video elements, modals etc.), that might be because you’re missing wp_footer() in your thme, because that action is not for rendering a <footer>, but instead it »[p]rints scripts or data before the closing body tag on the front end« (source).

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