WordPress：显示所有类别的帖子，每个类别最多5个帖子，并按日期排序？

Question

I am not sure if this has been answered before, but vigorous googling has not led me anywhere so far.

I have a wordpress site where I would like to display all posts as usual, ordered by date. However, instead of setting a limit on the total number of posts displayed, I would like to set a limit on each category.

For instance, if I have two categories FOO and BAR, I want WordPress to display all, but at most 5, posts from both FOO and BAR. The posts should still be ordered by date, and I mean that any post from FOO that was posted before one from BAR appears first and vice versa.

Specific problem: There is one post in the category FOO from last year, then 20 entries in BAR since then and now I am adding another post in the category FOO. Usually, Wordpress with a post limit of 10 would display this most recent FOO entry and 9 more BAR entries. However, I would like it to display both my FOO entries and the 5 most recent BAR entries. Only after I add 4 more FOO entries, the FOO entry from last year will no longer be displayed.

What is the best, most clean and maintainable way to achieve this?

I would be very grateful for any help.

Answer 1

Given that there seems no other solution that doing an insane amount of queries, I devised the following, added to functions.php.

function alter_query( $query ) {
    if ( $query->is_home() && $query->is_main_query() ) {
        $post_limit = floor(get_settings('posts_per_page')/2);      
        $the_posts = array();
        foreach (get_terms('category',array('hide_empty'=>1,'fields'=>'ids')) as $id) 
            $the_posts = array_merge( $the_posts, 
                get_posts( array(
                    'fields'      => 'ids',
                    'numberposts' => $post_limit,
                    'category'    => $id, 
                    'orderby'     => 'post_date')));
        $query->set('post__in',    $the_posts);
        $query->set('numberposts', -1);
        $query->set('orderby',     'post_date');
    }
}
add_action( 'pre_get_posts', 'alter_query' );

In this solution, I only fetch the ids of all relevant posts first, instead of all the contents and then perform a query to retrieve the actual data. I prefer this solution so far because I can use it without even touching my main loop, which is modified via the hook pre_get_posts.

I would still prefer a solution that is a little faster, i.e. one that only performs a single query.