Multisite, using switch_to_blog in filter

Question

I am programming a hook for ACF to get a list of posts from another site in a network.

so

switch_to_blog(1);

... do some WP_Query...

...list results in an array ...

restore_current_blog;

in a filter add_filter('acf/load_field/name=industries', 'acf_load_choices');

but the switch_to_blog is not working.

I can get raw results using the SQL within the WP_Query object. I can get the results if the current blog is 1 (as above) so I know my internal code is correct but not if the switch_to_blog is needed to do something.

Why is switch_to_blog not available in this context?

My two functions, the first works, the second doesn't

function acf_load_industry_pages( $field ) {

    // reset choices
    $field['choices'] = array();

    global $wpdb;

    $language = pll_current_language();
    switch_to_blog(1);
    $top_parent = pll_get_post('160', $language);
    restore_current_blog();

    $page_query=" SELECT wp0_posts.*
                 FROM wp0_posts  
                 LEFT JOIN wp0_term_relationships 
                    ON (wp0_posts.ID = wp0_term_relationships.object_id) 
                 WHERE wp0_posts.post_parent = ". $top_parent. "
                    AND (wp0_posts.post_type = 'page' ) 
                    AND (wp0_posts.post_status = 'publish') 
                 GROUP BY wp0_posts.ID 
                 ORDER BY wp0_posts.menu_order ASC";

    $pages = $wpdb->get_results( $page_query);

    if( is_array($pages) ) {

        foreach( $pages as $page ) {

            $field['choices'][ $page->ID ] = $page->post_title;

            $parent = $page->ID;
            $child_page_query=' SELECT wp0_posts.* 
                                    FROM wp0_posts  
                                LEFT JOIN wp0_term_relationships 
                                    ON (wp0_posts.ID = wp0_term_relationships.object_id) 
                                WHERE wp0_posts.post_parent ='. $parent.' 
                                    AND (wp0_posts.post_type = \'page\' ) 
                                    AND (wp0_posts.post_status = \'publish\') 
                                GROUP BY wp0_posts.ID 
                                ORDER BY wp0_posts.menu_order ASC
                                ';

            $child_pages = $wpdb->get_results( $child_page_query);

            if( is_array($child_pages) ) {
                foreach ($child_pages as $page) {
                    $field['choices'][$page->ID] = $page->post_title;
                }
            }

        }
    }


    // return the field
    return $field;

    }

    // in development


    function acf_load_industry_pages_wp_query( $field )
    {

    // reset choices
    $field['choices'] = array();

    global $wpdb;
    
    $language = pll_current_language();
    
    switch_to_blog(1);
    $top_parent = pll_get_post('160', $language);

    $args = array(
        'post_type' => 'page',
        'posts_per_page' => -1,
        'post_parent' => $top_parent,
        'lang' => $language,
    );

    $page_query = new WP_Query($args);

    if ($page_query->have_posts()) {
        while ($page_query->have_posts()) {
            $page_query->the_post();

            $field['choices'][get_the_ID()] = get_the_title();
        }
    }
    wp_reset_postdata();
    restore_current_blog();

    // return the field
    return $field;

    }

Answer 1

Did you use as follows (here $blog_id as 1):

 switch_to_blog( 1 );
 //Do stuff
 restore_current_blog();