get_post_meta in WP_Query

Question

If you will be pulling a lot of posts (or simply want to reduce the number of queries made), I’d recommend re-writing things a little bit.

First, build a filter function to modify the query you are about to make.

function filter_query_add_likes( $clauses, WP_Query $wp_query ) {
    if ( !is_admin() && !$wp_query->is_main_query() ) {
        global $wpdb;

        # Add your wanted meta value in as times_liked
        $clauses['fields'] .= ', IFNULL( meta_like.meta_value, 0 ) as times_liked ';

        # Join the postmeta field based on the post id and the key wanted
        # - this assumes you only have one times_liked meta for each post id!
        $clauses['join'] .= <<<SQL
 LEFT JOIN {$wpdb->prefix}postmeta AS meta_like ON meta_like.post_id = {$wpdb->prefix}posts.ID AND meta_like.meta_key = '_like_amount'
SQL;

    }
    return $clauses;
}

Next, use that filter right before you run your query to get your likes field back in each post.

function my_plugin_options() {
    # Same as what you did, just using heredoc
    echo <<<HTML
<p>Table of Likes</p>
</div>
<table>
<tr>
    <td>Post</td>
    <td>Number of Likes</td>
</tr>
HTML;


    $like_args = array(
        'post_type' => 'post',
        'order' => 'DES',
        'post_status' => 'publish'
    );
    # Set our new filter query to apply for this query
    add_filter('posts_clauses', 'filter_query_add_likes', 10, 2);

    $like_loop = new WP_Query( $like_args );

    # Remove our filter query to avoid touching other queries on accident
    remove_filter('posts_clauses', 'filter_query_add_likes', 10, 2);

    if ( $like_loop->have_posts() ) {
        while ( $like_loop->have_posts() ) {
            # using next_post like this pulls your posts out for easy access
            $current_post = $like_loop->next_post();

            # your times_like (from the filter) can now be accessed without
            # having to do an extra query with get_post_meta()
            $likes = $current_post->times_liked;
            # your title can be pulled right in if wanted
            $title = $current_post->post_title;

            # Draw your column
            echo <<<HTML
<tr>
    <td>{$title}</td>
    <td>{$likes}</td>
</tr>
HTML;

        }
    }

    # End the table
    echo "\r\n</table>";

}

This does a couple of things:

You now only use a single query to pull in all results that you want to show
You can easily pull whatever you want from the post object, including the number of times the post was liked.
If there is no likes count yet on a post, it will receive 0 due to the ISNULL call made when editing the fields clause.

Overall, much faster than using get_post_meta, especially if you are dealing with a lot of posts.

Related Posts: