If your WordPress plugin or theme has special functionality that is triggered by the “publishing” or other change to a page or post, then you will be using the transition_post_status hook. I had to experiment quite a bit with this hook to determine the keywords actually used for $new_status and $old_status, and now I’m sharing the complete list of my findings. Read on for a reference guide on what specific post transitions are called when any type of action is taken within the WordPress Admin. (Tested as of WordPress version 3.1)
In most cases, two separate transitions were triggered by one action, and in that case the first and second status keywords are separated by a line ( | ).
This pattern seems to hold for both ‘pages’ and ‘posts’, BUT custom post types don’t get the ‘new’ and ‘inherit’ status emitted on each change like the others.
|Action Taken||Old Status||New Status|
|Create new post||new||auto-draft|
|Wrote something in the new post||auto-draft||draft|
|Waited (autosave ran)||draft||draft|
|Saved draft||new | draft||inherit | draft|
|Saved and published for first time||new | draft||inherit | publish|
|Updated published post||new | publish||inherit | publish|
|Scheduled post for future publish||new | draft||inherit | future|
|Changed scheduled post to private||new | future||inherit | private|
|Set private future-post to new future-publish date||new | private||inherit | private|
|Sent regular, published post to trash||new | publish||inherit | trash|
|Permanently deleted post from trash||(Nothing)||(Nothing)|
|Sent privately scheduled post to trash||new | private||inherit | trash|
|Restored privately scheduled post from trash||new | trash||inherit | private|
|Restored regularly published post from trash||new | trash||inherit | publish|
|Made private scheduled post public||new | private||inherit | publish|
|Let the scheduled post reach it’s publication time||future||publish|
It seems like there should be an easier way to hook into specific types of post transitions. I wanted to trigger certain updates whenever a post was made public, and for that I need to separately hook into all of the following transitions: draft-to-publish, auto-draft-to-publish, private-to-publish, future-to-publish, trash-to-publish, etc.
Anyway, I hope that this is helpful!
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