Pass IDs to pre_get_posts query in function

Question

I am trying to pass the post ids to the function's query->set and function will return the posts.

add_action( 'pre_get_posts', 'query_booked_posts' );

function query_booked_posts( $query ) {
    if ( $condition ) { //the condition

    if ( is_home() && $query->is_main_query() )
    $results = $wpdb->get_col($wpdb->prepare( "SELECT booked_id FROM $wpdb->userbooking WHERE userid = %d",$current_user_id));

    foreach($results as $result){
    $results_separated = $result.',';
    }
    $query->set ('post__in', array($results_separated)); // pass results (post ids) to post__in

    return $query;
    }

}    

After this, the function returns nothing.

If I do $query->set ('post__in', array(45,121));, the query will return the posts of id 45 and id 121, so the query works fine.

But I want to make $results_separated pass the post ids like 45,121,132 to the query, and then $query->set ('post__in', array($results_separated)); will work correctly. How can I make this happen?

pre_get_posts reference

Answer 1

Except the extra array() over $results_separated, in my case I had to apply

if (!$query->is_main_query()) {
    return $query;
}

at the top of my function (found it in, otherwise, queries inside would be executed for several times and not properly. Comments in the answer helped me to figure this out.

Answer 2

I guess you have actually a PHP problem. When you do array($results_separated) you're basically creating an array from a string that looks like this: "12,114,56,". By doing that, PHP is creating an array like this:

array(
    0 => "12,114,56,"
)

And obviously WordPress cannot find any posts with such ID! What you want is actually an array like this:

array(
    0 => "12",
    1 => "114",
    2 => "56"
)

And actually that's what get_col() returns, so you just need to pass $results to set() function:

$query->set ( 'post__in', $results );

---

EDIT: Actually I realised that your problem is when you call $wpdb->get_col(...), because it's interfering with the $query you will execute later on... Those variables are using some other global variables that probably get overriden, and that's why you're not getting any results...