2

I'm creating a plugin that adds a custom feed. I am using a pre_get_posts filter to change the posts_per_page query var to -1 (to get all items of a custom post type). However, if I dump the $wp_query in the render function, posts_per_page remains the default. I tested also changing posts_per_rss to -1, and I do see that as changed in the query (though it, of course, doesn't have any effect on the resulting posts). I also tried changing my theme to a default one and testing, but I had the same results. Can anyone explain why I can't change the posts_per_page query var?

defined( 'ABSPATH' ) OR exit;

if(!class_exists('My_Custom_Feeds'))
{

    class My_Custom_Feeds { 

        protected $feed_slug = 'theslug';

        function __construct() {

            add_action( 'init', array($this, 'mcf_add_feed'));
            add_filter( 'pre_get_posts', array($this, 'mcf_pre_get_posts'));
        }

        function mcf_add_feed() {
            add_feed($this->feed_slug, array($this, 'mcf_render'));
        }

        function mcf_render(){

            //just output query to ensure it is as expected - but it's not
            global $wp_query;
            var_dump($wp_query);
            exit();
        }

        function mcf_pre_get_posts( $query ) {

            if ( $query->is_main_query() && $query->is_feed( $this->feed_slug ) ) {

                // modify query here to show all posts
                $query->set( 'posts_per_page', -1);
                $query->set( 'posts_per_rss', -1);
            }
        }
    }
}
if ( class_exists('My_Custom_Feeds') ){

    $my_custom_feeds = new My_Custom_Feeds();
}

Update one: Realized I was using add_filter instead of add_action for pre_get_posts. I've updated that, though I still see the same issue.

add_action( 'pre_get_posts', array($this, 'mcf_pre_get_posts'));

Update two (and final): Per @ialocin's answer, I realized changing the posts_per_page query var is futile since it is overwritten by the posts_per_rss option in a feed query (my scenario). So, the answer is to use a filter to alter that option. (-1 is not a valid posts_per_rss value, thus the arbitrary one used below.)

function mcf_posts_per_rss( $option_name ) {
    global $wp_query;
    if ( $wp_query->is_main_query() && $wp_query->is_feed( $this->feed_slug ) ) {
            return 100; //arbitrarily large value that, while not ideal, works for me
    }
    return $option_name;
}

Then in my plugin class constructor I added the following (and removed the pre_get_posts action):

add_filter( 'pre_option_posts_per_rss', array( $this, 'mcf_posts_per_rss') );
2

The init hook runs well before pre_get_posts so dumping the query at that point-- on init-- isn't going to reflect anything that will be done much later. I don't think there is anything wrong with your code, you misunderstand the sequence of actions. What you expect to happen isn't what actually happens.

  • Thanks for the response. So, is there another action that I should add the feed on other than init? Otherwise, it sounds like I will have to requery in my render function and reset the post data after. – Nicole Jun 18 '15 at 17:53
  • 1
    Adding the feed on init isn't the problem. Trying to dump $wp_query at that point is. The query will not be altered until later on pre_get_posts. I don't think the problem is your functionality but that you are trying to test that functionality based on a flawed premise. – s_ha_dum Jun 18 '15 at 18:00
  • Got it. But then my original question stands - why can't I change that query var? I continue to get only ten items rendered in the feed. – Nicole Jun 18 '15 at 18:49
1

posts_per_rss is not a WP_Query parameter. It is the name of the option that is saved into the database. It can be addresses via the pre_option_{$option_name}:

function wpse191824_posts_per_rss( $option_name ) {
    return 999;
}
add_filter( 'pre_option_posts_per_rss', 'wpse191824_posts_per_rss' );
  • Thanks! I'm marking yours as the answer as it sent me down the path to figuring out my issue. I was originally setting posts_per_rss simply as a test, but doing some searching around this option I found out that the posts_per_page query var is overwritten by it if the query is in a feed. I also discovered that -1 is apparently not a valid posts_per_rss value, so I had to set it to an arbitrarily higher value for some scenarios. Will update my original post with the valid code. – Nicole Jun 18 '15 at 21:50
  • My pleasure! You are right about the number. I'm guessing it is because the input at the form has min="1" set. Another thing, next time just post your solution as answer. It is how the system works. So you actually should do it - thanks. Then you can also always accept your own answer too. @Nicole – Nicolai Jun 18 '15 at 22:23
1

Per the discussion/help in this thread, below is the basic code that ended up working for my purposes. Setting the posts_per_page query var was a futile exercise since it is overwritten by the posts_per_rss option in a feed query (my scenario). posts_per_rss is not a query var and must be set a different way, thus the pre_option_posts_per_rss filter added. (-1 is not a valid posts_per_rss value, thus the arbitrary one used below.)

defined( 'ABSPATH' ) OR exit;

if(!class_exists('My_Custom_Feeds'))
{

    class My_Custom_Feeds { 

        protected $feed_slug = 'theslug';

        function __construct() {

            add_filter( 'pre_option_posts_per_rss', array( $this, 'mcf_posts_per_rss') );
            add_action( 'init', array($this, 'mcf_add_feed'));
        }

        function mcf_add_feed() {

            add_feed($this->feed_slug, array($this, 'mcf_render'));
        }

        function mcf_render(){

            //put rendering stuff here
            exit();
        }

        function mcf_posts_per_rss( $option_name ) {

            global $wp_query;
            if ( $wp_query->is_main_query() && $wp_query->is_feed( $this->feed_slug ) ) {
                return 100; //arbitrarily large value that, while not ideal, worked for my purposes
            }
            return $option_name;
        }
    }
}
if ( class_exists('My_Custom_Feeds') ) {

    //instantiate class
    $my_custom_feeds = new My_Custom_Feeds();
}

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