Check if post is being published for the first time, or is an already published post being updated

I am building an add-on to an events module that checks for availability, since there wasn’t a function for that in that module. Now that I have built the logic, there are three emails I will need to send:

• One if the post is being submitted for the first time (ie ‘New appointment’)
• One if the post has been published by the site admin, as normal users won’t be able to publish by themselves (ie ‘Your appointment has been approved’)
• One for if the post has been edited, AFTER it has been published already (ie ‘Your appointment has been edited’)

I have hooked into save_post and publish_post for those first two, but I want an entirely different email sent upon editing a PUBLISHED post. How can I test for whether the post is already published and this is just an edit, versus it being published for the first time?

Answers:

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Method 1

Hook into edit_post to catch changes. And take a look at wp_transition_post_status() which is called on inserts and updates:

function wp_transition_post_status($new_status, $old_status, $post) {
    do_action('transition_post_status', $new_status, $old_status, $post);
    do_action("{$old_status}_to_{$new_status}", $post);
    do_action("{$new_status}_{$post->post_type}", $post->ID, $post);
}

On publish you hook into

• draft_to_publish,
• pending_to_publish and
• auto-draft_to_publish.

For edits hook into publish_to_publish.

Example

A mini plugin that notifies all authors during post publish or edit.

<?php
/**
 * Plugin Name: (#56779) Notify authors
 */
add_action( 'transition_post_status', 'wpse_56779_notify_authors', 10, 3 );
function wpse_56779_notify_authors( $new_status, $old_status, $post )
{
    if ( 'publish' !== $new_status )
        return;

    $subject = 'publish' === $old_status
        ? __( 'Edited: %s', 'your_textdomain' )
        : __( 'New post: %s', 'your_textdomain' );

    $authors = new WP_User_Query( array( 'role' => 'Author' ) );
    foreach ( $authors as $author )
    {
        wp_mail(
            $author->user_email,
            sprintf( $subject, $post->post_title ),
            $post->post_content
            // Headers
            // Attachments
        );
        // Slow down
        sleep( 5 );
    }
}

Method 2

Use this….

function save_func($ID, $post,$update) {

   if($update == false) {
     // do something if its first time publish
   } else {
     // Do something if its update
   }
}

add_action( 'save_post', 'save_func', 10, 3 );

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0