I want to run wp_query on a separate php file for an ajax call

Question

For example:

Answer 1

You have to make the page that ajax calls a template page. Make a new page in your blog and assign the template. no headers no includes.

Answer 2

You have to include the file that has the Wordpress functions located on the main directory of the Wordpress Installation:

define('WP_USE_THEMES', false);  
require_once('../../../wp-load.php');

../../../ = path to the main directory on your installation

I found a nice tutorial about this here.

Answer 3

This worked for me, maybe it will help someone else.

My situation is I have a js file that uses getScript. In that script i have a bunch of .load() calls to a php file. At the top I place this.

if (file_exists("../../../wp-load.php"))
    {
    require_once("../../../wp-load.php");
    }

Change the ../ to how ever many directories your wp-load file is up.

Edit - Using WP 3.4.1

Answer 4

You can turn the template engine off and then include the header.
// Include WordPress
define('WP_USE_THEMES', false);
require_once('PATHHERE/wp-blog-header.php');