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Do you know that when you post data to a WordPress permalink, data field name might conflict with reserved query variables in WordPress, and end up a 404 not found response?

In my case I have a ‘name’ field that I want to post back to a permalink in my WordPress application, while I am absolutely sure the permalink is right, but I always get 404 response from WordPress. Through a few lines debugging I found the answer to this strange behaviour.

This is only applying to submit data back to a permalink, not a problem if data is submitted back to a file, as request of a file is not handled by WordPress.
When request is a permalink, the requested url will be parsed by WordPress, during the process, WordPress has a list of reserved query variable s to check against your request. If matches are found, then the values will be treated as variable values to query your blog post or page rather than user data, which very likely will end up not found error.

There are two reserved variable lists, public_query_vars and private_query_vars

var $public_query_vars = array('m', 'p', 'posts', 'w', 'cat', 'withcomments', 
'withoutcomments', 's', 'search', 'exact', 'sentence', 'debug', 'calendar', 'page', 'paged',
'more', 'tb', 'pb', 'author', 'order', 'orderby', 'year', 'monthnum', 'day', 'hour', 'minute',
'second', 'name', 'category_name', 'tag', 'feed', 'author_name', 'static', 'pagename',
'page_id', 'error', 'comments_popup', 'attachment', 'attachment_id', 'subpost',
'subpost_id', 'preview', 'robots', 'taxonomy', 'term', 'cpage', 'post_type');

var $private_query_vars = array('offset', 'posts_per_page', 'posts_per_archive_page',
'showposts', 'nopaging', 'post_type', 'post_status', 'category__in', 'category__not_in',
'category__and', 'tag__in', 'tag__not_in', 'tag__and', 'tag_slug__in', 'tag_slug__and',
'tag_id', 'post_mime_type', 'perm', 'comments_per_page');

All the words within these two lists are reserved, therefore should not be used as field name for user data. So you can see why I can not post a ‘name’ field as ‘name’ is a public query var.

Tags: WordPress