I’m looking to pass custom nav_menus through an RSS feed so I can grab them on other sites to create the same custom menu on multiple sites.
What I can’t figure out by looking through the database is how WP is storing the data it needs to know which items are parent>child related for hierarchy. How does it know to output the “child” pages as a separate ul even if they aren’t “officially” set as parent>child (from edit post screen), only visually in the Menus area?
I can look at just the post type of nav_menu_item in the database and the menu_order column lists the items in top to bottom order but nothing seems to reference the menu>submenu relationship.
Thanks for anything you can tell me.
Answers:
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Method 1
- Each nav menu item is stored a post type named
nav_menu_item. - The horizontal position is stored in the column
menu_order - The vertical position (hierarchy) is stored as post meta field named
_menu_item_menu_item_parentholding the parentnav_menu_itemID.
To create nested lists WordPress looks for _menu_item_menu_item_parent on each item, and if there is an item with that ID those posts will be grouped in a new sub list. That is basically what the class Walker_Nav_Menu does.
To illustrate that, use a little plugin:
<?php
/**
* Plugin Name: Inspect Nav Menu Items
* Plugin URI: http://wordpress.stackexchange.com/q/70872
*/
add_filter( 'wp_nav_menu_args', 'wpse_70872_inspect_nav_menu_items' );
function wpse_70872_inspect_nav_menu_items( $dummy = 1 )
{
if ( 'wp_nav_menu_args' === current_filter() )
{
add_action( 'shutdown', __FUNCTION__ );
return $dummy;
}
// If we made it so far this function was called on 'shutdown'.
$nav_items = get_posts(
array (
'numberposts' => -1,
'post_type' => 'nav_menu_item'
)
);
$out = array ();
foreach ( $nav_items as $nav_item )
{
$out[] = array (
// general post data
'post_data' => $nav_item,
// meta data
'meta' => get_post_custom( $nav_item->ID ),
// Name of the menu
'terms' => wp_get_object_terms( $nav_item->ID, 'nav_menu' ),
);
}
print '<pre>' . esc_html( var_export( $out, TRUE ) ) . '</pre>';
}
The result might look like this:
array (
0 =>
array (
'post_data' =>
stdClass::__set_state(array(
'ID' => 695,
'post_author' => '1',
'post_date' => '2012-10-29 23:24:13',
'post_date_gmt' => '2012-10-29 23:24:13',
'post_content' => ' ',
'post_title' => '',
'post_excerpt' => '',
'post_status' => 'publish',
'comment_status' => 'open',
'ping_status' => 'open',
'post_password' => '',
'post_name' => '695',
'to_ping' => '',
'pinged' => '',
'post_modified' => '2012-10-29 23:24:13',
'post_modified_gmt' => '2012-10-29 23:24:13',
'post_content_filtered' => '',
'post_parent' => 0,
'guid' => 'http://wpse.mu.wp/?p=695',
'menu_order' => 9,
'post_type' => 'nav_menu_item',
'post_mime_type' => '',
'comment_count' => '0',
'filter' => 'raw',
)),
'meta' =>
array (
'_menu_item_type' =>
array (
0 => 'taxonomy',
),
'_menu_item_menu_item_parent' =>
array (
0 => '693',
),
'_menu_item_object_id' =>
array (
0 => '12',
),
'_menu_item_object' =>
array (
0 => 'category',
),
'_menu_item_target' =>
array (
0 => '',
),
'_menu_item_classes' =>
array (
0 => 'a:1:{i:0;s:0:"";}',
),
'_menu_item_xfn' =>
array (
0 => '',
),
'_menu_item_url' =>
array (
0 => '',
),
),
'terms' =>
array (
0 =>
stdClass::__set_state(array(
'term_id' => '105',
'name' => 'Test 1',
'slug' => 'test-1',
'term_group' => '0',
'term_taxonomy_id' => '106',
'taxonomy' => 'nav_menu',
'description' => '',
'parent' => '0',
'count' => '9',
)),
),
),
1 =>
array (
'post_data' =>
stdClass::__set_state(array(
'ID' => 694,
'post_author' => '1',
'post_date' => '2012-10-29 23:24:12',
'post_date_gmt' => '2012-10-29 23:24:12',
'post_content' => ' ',
'post_title' => '',
'post_excerpt' => '',
'post_status' => 'publish',
'comment_status' => 'open',
'ping_status' => 'open',
'post_password' => '',
'post_name' => '694',
'to_ping' => '',
'pinged' => '',
'post_modified' => '2012-10-29 23:24:12',
'post_modified_gmt' => '2012-10-29 23:24:12',
'post_content_filtered' => '',
'post_parent' => 0,
'guid' => 'http://wpse.mu.wp/?p=694',
'menu_order' => 8,
'post_type' => 'nav_menu_item',
'post_mime_type' => '',
'comment_count' => '0',
'filter' => 'raw',
)),
'meta' =>
array (
'_menu_item_type' =>
array (
0 => 'taxonomy',
),
'_menu_item_menu_item_parent' =>
array (
0 => '693',
),
'_menu_item_object_id' =>
array (
0 => '11',
),
'_menu_item_object' =>
array (
0 => 'category',
),
'_menu_item_target' =>
array (
0 => '',
),
'_menu_item_classes' =>
array (
0 => 'a:1:{i:0;s:0:"";}',
),
'_menu_item_xfn' =>
array (
0 => '',
),
'_menu_item_url' =>
array (
0 => '',
),
),
'terms' =>
array (
0 =>
stdClass::__set_state(array(
'term_id' => '105',
'name' => 'Test 1',
'slug' => 'test-1',
'term_group' => '0',
'term_taxonomy_id' => '106',
'taxonomy' => 'nav_menu',
'description' => '',
'parent' => '0',
'count' => '9',
)),
),
),
// … and so on. It is a long list.
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