4

I am working on the design of a blog with the below(just a sample) category hierarchy.

                                          PARENT
                                             |
                     |------------------------------------------------|
                   Food                                           Fashion
                     |                                                |
          |---------------------|                       |---------------------|
      European                Asian                  European               Asian
          |                     |                       |                     |
    |---------|           |-----------|             |--------|           |--------|
Italian    French      Chinese    Japanese       Italian  French     Chinese   Japanese

On the homepage, my client wants to display the three last posts of all the level 4 children, hence:

  • The last three posts of Parent>Food>European>Italian
  • The last three posts of Parent>Food>European>French
  • The last three posts of Parent>Food>Asian>Chinese, etc.
  • etc.

My first attempt was like this:

$allPosts = new WP_Query('cat=20, 21, 24, 22, 23, 25, 75, 84, 79, 85, 83, 96, 95, 97, 65, 68, 107, 48, 49&showposts=100&order=ASC');

According to a debugging plugin, 18 queries were called on the page but I realised that such a call makes no sense for what I want because if a category has 2000 posts, the 100 posts this line will retrieve will all be from the same category.

I therefore split the calls, like this:

$italianFood = new WP_Query('cat=20&showposts=3&order=DESC');
$italianFashion = new WP_Query('cat=21&showposts=3&order=DESC');
$frenchFood = new WP_Query('cat=24&showposts=3&order=DESC');
$frenchFashion = new WP_Query('cat=22&showposts=3&order=DESC');

This works but after calling ALL categories, the number of query calls to the database went up to 260!

I will cache the page with a plugin, but do I really have to fire 260+ DB calls to achieve what I want?

3
  • In the meantime, I tried "get_posts" instead of "WP_Query" as in get_posts("post_type=post&numberposts=3&category=20) which apparently reduced the number of calls from 260 to 220. – WPRookie82 Jul 20 '14 at 11:39
  • 260 seems high, had you tried dumping the list of calls and narrowing down what exactly blows it up? get_posts()/WP_Query are nearly identical (former wraps latter) btw. – Rarst Jul 20 '14 at 11:45
  • I have 19 countries, all of which are divided in Food and Fashion so a total of 38 Level-4 categories and hence a total of 38 WP_Query (or get_posts) calls. It seems for every post, the page is calling wp_posts, wp_terms and wp_postmeta, albeit joined for posts in the same category : WHERE ID IN (1208,1207,1206); – WPRookie82 Jul 20 '14 at 11:50
2

You could just write your own query, too. That way, it's one query per category:

global $wpdb;

$query = '
SELECT wpp1.*
FROM ' . $wpdb->posts . ' AS wpp1
LEFT JOIN ' . $wpdb->term_relationships . ' AS wptr1 ON wptr1.object_id = wpp1.ID
WHERE post_type = %s
AND post_status = %s
AND wptr1.term_taxonomy_id = %d
ORDER BY wpp1.post_date DESC
LIMIT %d
';

$query = $wpdb->prepare(
    $query,
    // Args: post type, post status, term taxonomy ID, number of posts
    'post', 'publish', 80, 3
);

$posts = $wpdb->get_results(
    $query,
    ARRAY_A
);
1
  • That is indeed what I ended up doing, reducing the calls from 260 to 49. In theory I also reduced them to only 12 queries but it's by using one big query with a WHERE ID IN(SELECT) which I preferred to avoid. I asked about this approach some three weeks ago and I received some very logical answers why to avoid it but for this particular case I had no alternative: wordpress.stackexchange.com/questions/151837/…. – WPRookie82 Jul 23 '14 at 7:16

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