Pass results of custom query to loop - when writing a plugin

Question

This is similar to this question: How to change a custom query into a standard loop? - but I want to do this while writing a plugin, not writing a theme.

I need to be able to run a custom query (using regular old sql), and set the result as the post available for the loop. I am writing a plugin, so template tags, foreach loops, etc are not what I'm looking for. I just want to run my sql query, pick the correct row, and tell wordpress to use this as the post for the loop.

Here's what I've tried so far:

add_filter( 'pre_get_posts' , 'customQuery' );

function customQuery() {
  global $wpdb;
  $sql = "some sql here";
  $safequery = $wpdb->prepare($sql);

  $queryResults = $wpdb->get_results($safequery);
}

That works for retrieving my expected results. The variable $queryResults holds the correct data. After that line, I've tried a couple of things, neither of which worked.

...snip...
global $post;
$post = $queryResults[0]; //since it is an array, and I just need the first result

That didn't work. Or rather, if I do a var_dump immediately after that line, $post is what I expect, but it seems to be reset somewhere down the line as I get a 404 when the page actually renders.

I also tried:

...snip...
global $post;
$post = $queryResults[0];
setup_postdata($post); 

Same outcome. If I check the values of variables right away, I see what I expect. With the second example I even tried, just for fun, running things like the_title(); which works (but doesn't help me because, again, I'm trying to write a plugin, not a theme). But when I let the page run through to rendering, I get a 404.

I'm sure I'm just missing something simple that'll let me pass my results to the loop from the plugin layer. Any suggestions? Thanks.

Answer 1

Found the correct hook to use. This intercepts the query and lets me modify it for my own purposes:

add_filter('posts_request', 'changeQuery');

function changeQuery($query) {
  $query = 'my new sql query here';
  return $query;
}