Using WordPress ‘posts_fields’ PHP filter

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The posts_fields filter allows you to modify the SELECT clause of the query when retrieving posts from the WordPress database.

Usage

add_filter('posts_fields', 'your_custom_function', 10, 2);

function your_custom_function($fields, $query) {
    // your custom code here
    return $fields;
}

Parameters

  • $fields (string): The SELECT clause of the query.
  • $query (WP_Query): The WP_Query instance, passed by reference.

More information

See WordPress Developer Resources: posts_fields

Examples

Add Post Thumbnail URL to the Query

Add the post thumbnail URL to the post fields by using a JOIN and SELECT statement.

add_filter('posts_fields', 'add_post_thumbnail_url', 10, 2);

function add_post_thumbnail_url($fields, $query) {
    global $wpdb;
    $fields .= ", CONCAT('$wpdb->postmeta.meta_value') as post_thumbnail_url";
    return $fields;
}

Add Custom Meta Field to the Query

Add a custom meta field ‘price’ to the post fields.

add_filter('posts_fields', 'add_price_to_fields', 10, 2);

function add_price_to_fields($fields, $query) {
    global $wpdb;
    $fields .= ", $wpdb->postmeta.meta_value as price";
    return $fields;
}

Select Only Post Titles and IDs

Modify the query to select only post titles and IDs.

add_filter('posts_fields', 'select_post_titles_and_ids', 10, 2);

function select_post_titles_and_ids($fields, $query) {
    global $wpdb;
    $fields = "$wpdb->posts.ID, $wpdb->posts.post_title";
    return $fields;
}

Add Comment Count to the Query

Include the comment count of each post in the query.

add_filter('posts_fields', 'add_comment_count', 10, 2);

function add_comment_count($fields, $query) {
    global $wpdb;
    $fields .= ", COUNT($wpdb->comments.comment_ID) as comment_count";
    return $fields;
}

Select Only Published Posts with a Specific Tag

Modify the query to select only published posts with a specific tag.

add_filter('posts_fields', 'select_published_posts_with_tag', 10, 2);
function select_published_posts_with_tag($fields, $query) {
    global $wpdb;
    $fields .= " AND $wpdb->term_relationships.term_taxonomy_id = 10";
    return $fields;
}