Assign Json file to WP_Query

Found the solution. $wp_query returns an array of objects. Therefore when decoding the json set teh second parameter to false like so

 json_decode($str, false);

Then assign the returned values to object vars
like so:

if (is_file($file)){
    $str = file_get_contents($file);    
    $my_query_raw = json_decode($str, false);
    $my_query1 = null;
    $wp_query = null;
    $my_query1 = new WP_Query;
    $posts_son = ($my_query_raw->posts);

    $my_query1->query = $my_query_raw->query;
    $my_query1->posts = $posts_son;
    $my_query1->request = $my_query_raw->posts;
    $my_query1->post_count = count($my_query_raw->posts);

    $found_posts = $my_query_raw->found_posts;
    $max_num_pages = $my_query_raw->max_num_pages;

    if ( isset($found_posts)) $my_query1->found_posts = $my_query_raw->$found_posts;
    if ( isset($max_num_pages)) $my_query1->max_num_pages = $my_query_raw->$max_num_pages;

//assign to $wp Query
$wp_query = $my_query1;
        }