Cannot save custom metabox data - wordpress

Question

I have made a custom metabox in a custom post type. My custom metabox includes two radio buttons. But no matter what I do, I'm not able to save data in my database. Wordpress saves it's data in the "wp_postmeta" but not the custom data that I wanted to save. Here's my code:
function wp_add_custom_meta_boxes(){
add_meta_box("custom_meta", "Settings", "wp_meta_box_callback", "images", "normal");
}
add_action("add_meta_boxes", "wp_add_custom_meta_boxes");
function wp_meta_box_callback($post){
wp_nonce_field(basename(__FILE__), "wp_custom_image_nonce");
?>
<div class="meta-row">
<div class="meta-th">
<p>Should this image show on the main page ?</p>
</div>
<div class="meta-td">
<label for="yes">Yes</label>
<input id="yes" type="radio" name="on_mainpage" value="true">
<label for="no">No</label>
<input id="no" type="radio" name="on_mainpage" value="false">
</div>
</div>
<?php
}
function wp_save_meta_info($post_id){
if(!wp_verify_nonce("wp_custom_image_nonce", basename(__FILE__))){
return;
}
if(defined("DOING_AUTOSAVE") && DOING_AUTOSAVE){
return $post_id;
}
if(isset($_POST['on_mainpage'])){
update_post_meta($post_id, "show_on_mainpage", $_POST['on_mainpage']);
}
}
add_action("save_post", "wp_save_meta_info");
I have 1 more question. Does update_post_meta() requires some existing data in the database to be updated or does it automatically saves the data in the database if it doesn't exists ?
Thanks in advance :)

Answer 1

You have a typo in your update post meta function
function wp_save_meta_info($post_id){
if(!wp_verify_nonce($_POST["wp_custom_image_nonce"], basename(__FILE__))){
return;
}
if(defined("DOING_AUTOSAVE") && DOING_AUTOSAVE){
return $post_id;
}
if(isset($_POST['on_mainpage'])){
update_post_meta($post_id, "show_on_mainpage", $_POST['on_mainpage']);
}
}
Also just to point out there is a custom save_post hook for custom post types
the hook is called -- save_post_yourpostypename so
add_action("save_post_posttype", "wp_save_meta_info");
Otherwise you will need to check its the correct post type within the function, or have unique nonce names throughout your custom post types. Also i'd recommend using a different action for your nonces, something descriptive and unique would be better if you are debugging some time in the future
update_post_meta() will create a meta entry for your field name if it doesn't exist so developers prefer it to add_post_meta() when there should only be 1 meta entry for that field name, i.e. the data should be updated on post save rather than a new meta entry created. You can see your postmeta entries on the postmeta db table.