setup_postdata in "loop-handling" php file called via $.ajax

Question

I'm calling a "loop handler" kind of php file that opens a loop with WP_Query.

Inside the foreach loop I want to use the show_postdata function. I'm aware of the global $post aspect of this function. I tried placing the global $post everywhere in that php file without success though.

I get an error 500 server error with noch detailed error message in the catch part.

When I use the class to get data on the server inside a template it works.

This is my AJAX call:

    $.ajax({
    type       : "GET",
    data       : {numPosts : numPosts, postTypes : postTypes, template : template, postID : null, filterArgs : filterArgs, fields: fields, inclMeta : inclMeta, imgFields : imgFields },
    dataType   : "html",
    url        : bfApp.setWPUrl + "/bfLoopHandler.php",
    beforeSend : function(){
    },
    success    : function(data){

        if (typeof(callbackSuccess) == "function") {
            callbackSuccess(data);
        }

    },
    error     : function(jqXHR, textStatus, errorThrown) {

        if (typeof(callbackError) == "function") {
            callbackError(jqXHR, textStatus, errorThrown);
        }

    }
});

This is an excerpt from the php file up to the point where show_postdata is called:

class bfLoop {
public function getData($postIDs, $postTypes, $numPosts, $filterArgs, $template, $fields, $inclMeta, $imgFields, $inclCats) {

    global $post;

    define('WP_USE_THEMES', false);
    $parse_uri = explode( 'wp-content', $_SERVER['SCRIPT_FILENAME'] );
    require_once( str_replace('index.php', '', $parse_uri[0]) . 'wp-load.php' );

    // Argumente setzen
    if ($postIDs == null || $postIDs == 0) {
        $args = array( 'post_type' => $postTypes, 
                       'post_status' => array('publish'),
                       'posts_per_page' => $numPosts, 
                       'meta_query' => $filterArgs,
                       'fields' => $idsOnly );
    } else {
        if (is_array($postIDs)) {
            $args = array(
            'post__in' => $postIDs,
            'post_type' => 'any');                  
        } else {
            $args = array(
            'p' => $postIDs,
            'post_type' => 'any');                
        }
    }

    $loop = new WP_Query( $args );  

        $retArray = array();

        $posts = $loop->get_posts();   
        foreach ( $posts as $post ) {

            try {
               setup_postdata( $post ); 
            } catch(Exception $e) {
                //return "AFTER";
                return "W:" . $e->getMessage();
            } ......

Answer 1

Solved by getting author, post_date, permalink & excerpt manually without setup_postdata:

        $excerpt = myCustomExcerptFunction($post, 35);
        $post->post_excerpt = $excerpt;

        // Permalinks
        $post->post_permalink = get_post_permalink($post->ID);

        // Author
        $authorObjekt = get_userdata($post->post_author);
        $post->post_author_displayname = $authorObjekt->data->display_name;
        $post->post_author_nicename = $authorObjekt->data->user_nicename;

        // Date
        $post->post_date_wpformat = date_i18n( get_option( 'date_format' ),