Wordpress unique checkbox - wordpress

Question

I have created a custom field "headline" in posts that is handled by a checkbox. Now I want that when the post is saved and the checkbox is checked, all "headline" checkboxes are emptied in the other posts. If this works correctly there should only be one other post with that checkbox checked.
function createHeadlineField()
{
$post_id = get_the_ID();
if (get_post_type($post_id) != 'post') {
return;
}
$value = get_post_meta($post_id, '_headline_field', true);
wp_nonce_field('headline_nonce_'.$post_id, 'headline_nonce');
?>
<div class="misc-pub-section misc-pub-section-last">
<label><input type="checkbox" value="1" <?php checked($value, true, true); ?> name="_headline_field" /><?php _e('This post is the top Story', 'pmg'); ?></label>
</div>
<?php
}
function saveHeadlineField($post_id)
{
if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) {
return;
}
if (
!isset($_POST['headline_nonce']) ||
!wp_verify_nonce($_POST['headline_nonce'], 'headline_nonce_'.$post_id)
) {
return;
}
if (!current_user_can('edit_post', $post_id)) {
return;
}
if (isset($_POST['_headline_field'])) {
update_post_meta($post_id, '_headline_field', $_POST['_headline_field']);
} else {
delete_post_meta($post_id, '_headline_field');
}
}
Has anybody a clue how to do that? I guess I have to query the posts for posts with _headline_field values and delete these before updating the actual post.
thx

Answer 1

so if u want to query the posts with the metakey Headline u can do something like that:
$posts = array();
$query = new WP_Query(array('meta_key' => Headline, 'meta_value'=>YOURVALUE, 'posts_per_page' => LIMIT (-1 for endless)))
if ($query->have_posts()) {
while ($query->have_posts()) {
$query->the_post();
$posts[] = $query->post;
}
wp_reset_postdata();
}
return $posts;

Answer 2

I tried to do it like that:
if (isset($_POST['_headline_field'])) {
//query posts with custom field selected
$args = array ( 'meta_key' => '_headline_field', 'meta_value' => '1', LIMIT -1 );
$headline_query = new WP_Query( $args );
if ( have_posts() ):
while ( have_posts() ) :
$headline_query->the_post();
$headline_query->delete_post_meta(get_the_ID(), '_headline_field');
endwhile;
endif;
update_post_meta($post_id, '_headline_field', $_POST['_headline_field']);

Answer 3

Ok, found a solution.
I just used the "delete_post_meta_by_key()" function to erase alle post meta with the key _headline_field before writing the new value into the DB.
if (isset($_POST['_headline_field'])) {
delete_post_meta_by_key( '_headline_field' );
update_post_meta($post_id, '_headline_field', $_POST['_headline_field']);
}