register multiple post types on one menu entry

Question

Case:

I register_post_type() 3 different CPTs¹⁾

Example: 3 post types named party, event, location. The other needed arguments in the array are left out.

register_post_type(
     'party'
    ,array( 
        'show_in_menu' // true (for main) or "edit.php?post_type=party (for subentries)
     )
);

• Then I set the 'show_in_menu' argument for the first CPT item (a.k.a "party") to true
• The other items get set 'show_in_menu' to 'edit.php?post_type=party

Result:

What's the point with this? What I expected was that I get "Add New" menu items for all of them, not only for the main CPT.

How would I do set the arguments to not only get list views, but single new/edit screens as well?

Notes:

I know, that I got an Add New button in the list view on top next to the title, but I want to know how I could add these links to the admin menu items.

I also know that I can work around with

add_submenu_page(
     "edit.php?post_type=party"
    ,"Add New"
    ,"Add New"
    ,"post-new.php?post_type=party"
);

but I'm not interested in the work around. I want to know how this is thought to work out of the box.

^{1) CPT = short for custom post type}

Answer 1

Customizing the menu this way is as for as I can tell, not very friendly. What I had to do recently was custom built the submenu item using remove_submenu_page for all the sub menu items and then add them in the order I wanted using add_submenu_page.

A simple example

 //this was first sub-menu item I did not want it #1
 remove_submenu_page( 'edit.php?post_type=test', 'edit.php?post_type=test' );

 // add the actual sub-menu item I wanted as #1
 add_submenu_page('edit.php?post_type=hello','Hello', 'Hello', 'manage_options', 'my_hello', 'my_hello_options');

//re-add the orginal #1 item removed above so it is now the #2 item
 add_submenu_page('edit.php?post_type=test','Edit Test', 'Edit Test', 'manage_options', 'edit.php?post_type=test');

---

Edit: If you plan on using the menu_order filter, it's pretty simple to get the filter working: Just add this line before it. Else it would skip the menu_order filter: add_filter( 'custom_menu_order', '__return_true' );.