$wp_query and WP_QUERY - same arguments, different results - wordpress

Question

I spend this whole day trying to figure out a problem with a combination of a custom query and custom post types. This is my last resort...
The setting
I wrote a plugin that introduces some custom post types to my WordPress. To display them in the main query I hooked them into the query like this:
function add_cpt_to_query( $query ) {
*some code...*
// add custom post types to query
if ( !( is_admin() || is_post_type_archive() || is_page() ) && $query->is_main_query() ) {
$query->set('post_type', array_merge( array('post'), $cpt ) );
}
}
add_action('pre_get_posts','add_cpt_to_query');
In my theme on the other hand I setup ajax pagination like this:
function setup_pagination() {
global $wp_query;
$max_pages = $wp_query->max_num_pages;
$current_page = ( $wp_query->paged > 1 ) ? $wp_query->paged : 1;
$ajaxurl = admin_url( 'admin-ajax.php' );
wp_register_script( 'ajax-pagination', get_template_directory_uri() .'/js/dummy.js', array('jquery'), '', true);
wp_localize_script( 'ajax-pagination', 'ajaxpagination', array(
'max_pages' => $max_pages,
'current_page' => $current_page,
'ajaxurl' => $ajaxurl,
'query_vars' => $wp_query->query_vars
));
wp_enqueue_script( 'ajax-pagination' );
}
add_action( 'wp_enqueue_scripts', 'setup_pagination' );
function pagination() {
$query = $_POST['query_vars'];
$query['paged'] = $_POST['next_page'];
/*
$query = array(
'paged' => 2,
'post_type' => array('post', 'custom_post_type_1', 'custom_post_type_2' )
);
*/
$posts = new WP_Query( $query );
$GLOBALS['wp_query'] = $posts;
// Start the loop.
while ( have_posts() ) : the_post();
?>
*some code...*
<?php endwhile;
die();
}
add_action( 'wp_ajax_nopriv_ajax_pagination', 'pagination' );
add_action( 'wp_ajax_ajax_pagination', 'pagination' );
and the script part:
$.ajax({
url: ajaxpagination.ajaxurl,
type: 'post',
data: {
action: 'ajax_pagination',
query_vars: ajaxpagination.query_vars,
next_page: parseInt(ajaxpagination.current_page) + 1
}
});
The problem
If I pass the query_vars array I get from $wp_query with the altered 'paged' value back to WP_QUERY, it returns the wrong set of posts. It looks like, that WP_QUERY does not account for the cpts in the loop. Though these cpts are mentioned in the 'post_type' of the query_vars array and thereby passed along to the new WP_QUERY.
When I manually set 'post_type' and only pass this argument, it works as intended. The aspect that blows my mind is, that the resulting query_vars used in the ajax call to WP_QUERY are exactly the same, but only when I manually set 'post_type' the pagination works as it should.
I dont know if this was a somewhat understandable explanation, but I'm thankful for every idea that could help me out. Big THX!

Answer 1

Ok... I got it now.
I made a mistake in wp_localize_script(). The query_vars should be a json-string, I on the other hand just passed the array itself. My code above has to be altered in two lines:
function mk_setup_pagination() {
...
wp_localize_script( 'ajax-pagination', 'ajaxpagination', array(
...
'query_vars' => json_encode($wp_query->query_vars) <- convert to json-string
));
...
}
function mk_pagination() {
$query = json_decode( stripslashes( $_POST['query_vars'] ) , true); <- convert json-string to array
...
Works like a charm now. :)
btw: the code is based on a tutorial by wpmudev.org: Loading WordPress Posts Dynamically With AJAX