Show one post per author and order by custom field

Question

I display one post per author with function below and works fine, but is possible order by custom field?

<?php
add_filter('posts_groupby', 'author_groupby');
function author_groupby($groupby)
{
 global $wpdb;
 $author_groupby = "{$wpdb->posts}.post_author";
    if(preg_match("/$author_groupby/", $groupby)) {
    // grouping we need is already there
    return $groupby;
  }
  if(strlen(trim($groupby) == 0)) {
    // groupby was empty, use ours
    return $author_groupby;
  }
  return "$groupby, $author_groupby";
}

I've tried with code below but do not works:

...
$author_groupby = "{$wpdb->posts}.post_author 
AND pm.meta_key = 'KEY' 
ORDER BY pm.meta_value DESC Limit 0,1";
...

Thanks

Answer 1

You use a AND statement after a GROUP BY statement. That wont work.

Try altering the WHERE statement (posts_where_paged filter) to add the AND pm.meta_key = 'KEY' line.

Additionally you can use the posts_orderby filter to alter the ORDER BY.

EDIT

You can find some additional information here.

Answer 2

There is a posts_orderby filter that works like the posts_groupby filter you are already using. I don't see the point of trying to write the code since I don't know what your key is.

To make the orderby work you may need filters on posts_fields and/or posts_joins as well.

I don't know that your question is precise enough to give a better answer.

http://codex.wordpress.org/Custom_Queries