Get list of all Grandchild Pages

Question

I have the following page hierarchy, all of which are under a top page (TOP) with ID = 1:

• mid1
  • gc1
  • gc2
• mid2
  • gc3
  • gc4

I would like to make submit WP_Query query that will return random pages that are grandchildren of TOP - in this example, I want to randomly select from gc1, gc2, gc3 and gc4, but exclude mid1 and mid2. What is the best way to do this?

Answer 1

My current idea is:

1. Use get_pages to get all of the descendants of TOP and put the IDs in an array arrayAll.
2. Then run get_pages again with parent=1 to get just the direct children of TOP. Put these in array arrayChildren.
3. Run in php arrayGrandchildren = array_diff(arrayAll, arrayChildren) to get a list of all pages from the first array (which contains all descendants of TOP) that do not include the direct children.
4. In WP_Query, set 'post_in=arrayGrandchildren&order=rand' to get random posts from the list of grandchildren.