How to modify this function to exclude also the post belonging to a specific category?

Question

I am very new in WordPress development and I have the folglowing problem.

I use this function (declared into the functions.php file of my theme) to modify the main query in such a way that the post having a specific tag are not displayed in my homepage:

function exclude_featured_tag_and_legacy_posts( $query ) {

    $tagId = get_tag_ID("featured");
    //echo("Featured Tag Id: + $tagId");

    if ( $query->is_home() && $query->is_main_query() ) {
        //$query->set( 'tag__not_in', 'array(ID OF THE FEATURED TAG)' );

        $query->set( 'tag__not_in', array($tagId));
    }

}
add_action( 'pre_get_posts', 'exclude_featured_tag' );

As you can see this function is executed after the main query creation but before its executions and it modify the main query for the exclusion of the posts that have the tag named featured

Ok, it seems work fine. Now my problem is. How can I further modify my main query so that is also excluded the posts belonging to a specific category?

So I want that is excluded both the posts having the featured tag and the posts belonging to the legacy category.

Can you help me?

Answer 1

pre_get_posts and WP_Query uses the exact same parameters, so if you need to know which parameters you can use with pre_get_posts, simply visit the WP_Query page in the codex.

There is another trick which you can use to get all the parameters (query_vars) you can use. Just add this on the page that you need to get the query_vars from, refresh the page, and this function will print out all the query_vars you can use with pre_get_posts and WP_Query

<?php global $wp_query; ?>
    <pre><?php var_dump($wp_query->query_vars); ?></pre>
<?php

To exclude a category, you can either use cat or category__not_in. Both take category ID's, cat take integers and category__not_in an array. So one of the following will do in your function

$query->set( 'category__not_in', array(ARRAY OF CAT ID's));

OR

$query->set( 'cat', 'ID's OF CAT');

You just have to make sure, your callback function in add_action and your actual function name does not match. exclude_featured_tag must be exclude_featured_tag_and_legacy_posts

Answer 2

Please check the category parameters in the WP_Query documentation.