Ticket #3460: add_to_default_cat_posts_that_only_exist_in_deleted_cat.diff

wp-admin/admin-db.php

@@ -154 +154 @@
         global $wpdb;
 
         $cat_ID = (int) $cat_ID;
+        $default_cat = get_option('default_category');
 
         // Don't delete the default cat.
         if ($cat_ID == get_option('default_category'))
@@ -164 +165 @@
         $parent = $category->category_parent;
 
         // Delete the category.
-        $wpdb->query("DELETE FROM $wpdb->categories WHERE cat_ID = '$cat_ID'");
+        if ( !$wpdb->query("DELETE FROM $wpdb->categories WHERE cat_ID = '$cat_ID'") )
+                return 0;
 
         // Update children to point to new parent.
         $wpdb->query("UPDATE $wpdb->categories SET category_parent = '$parent' WHERE category_parent = '$cat_ID'");
 
-        // TODO: Only set categories to general if they're not in another category already
-        $default_cat = get_option('default_category');
-        $wpdb->query("UPDATE $wpdb->post2cat SET category_id='$default_cat' WHERE category_id='$cat_ID'");
+        // Only set posts and links to the default category if they're not in another category already
+        $posts = $wpdb->get_col("SELECT post_id FROM $wpdb->post2cat WHERE category_id='$cat_ID'");
+        $only_in_deleted = array();
+        foreach ( (array) $posts as $post_id ) {
+                $other_cat_count = $wpdb->get_var("SELECT COUNT(*) FROM $wpdb->post2cat WHERE category_id <> '$cat_ID' AND post_id = '$post_id'");
+                if ( 0 == $other_cat_count ) // exists only in the to-be-deleted category
+                        $only_in_deleted[] = $post_id;
+        }
 
+        if ( $only_in_deleted ) {
+                $only_in_deleted = implode(',', $only_in_deleted);
+                $wpdb->query("UPDATE $wpdb->post2cat SET category_id='$default_cat' WHERE category_id='$cat_ID' AND post_id IN($only_in_deleted)");
+        }
+
+        // Now, all remaining posts in $cat_ID should exist in another category, so we can do:
+        $wpdb->query("DELETE FROM $wpdb->post2cat WHERE category_id='$cat_ID'");
+
         wp_cache_delete($cat_ID, 'category');
         wp_cache_delete('all_category_ids', 'category');