Last modified: 2014-07-20 13:05:09 UTC
Example: http://commons.wikimedia.org/wiki/Category:Cultural_heritage_monuments_in_Dari%C3%A9n_Province This category was created by BotMultichill to extend the category tree. However, querying it using the api will not show the category: http://commons.wikimedia.org/w/api.php?action=query&list=allcategories&acprop=hidden&acfrom=Cultural%20heritage%20monuments%20in%20Dari This happens because, while there /is/ a Page row: mysql> select * from page where page_namespace=14 and page_title>="Cultural_heritage_monuments_in_Dari" limit 1; +----------+----------------+-------------------------------------------------+-------------------+--------------+------------------+-------------+----------------+----------------+-------------+----------+-----------------------+ | page_id | page_namespace | page_title | page_restrictions | page_counter | page_is_redirect | page_is_new | page_random | page_touched | page_latest | page_len | page_no_title_convert | +----------+----------------+-------------------------------------------------+-------------------+--------------+------------------+-------------+----------------+----------------+-------------+----------+-----------------------+ | 21211737 | 14 | Cultural_heritage_monuments_in_Darién_Province | | 0 | 0 | 1 | 0.721362456992 | 20130526075638 | 77704695 | 125 | 0 | +----------+----------------+-------------------------------------------------+-------------------+--------------+------------------+-------------+----------------+----------------+-------------+----------+-----------------------+ there is no entry in the category table: mysql> select * from category where cat_title>="Cultural_heritage_monuments_in_Dari" limit 1; +----------+------------------------------------------+-----------+-------------+-----------+------------+ | cat_id | cat_title | cat_pages | cat_subcats | cat_files | cat_hidden | +----------+------------------------------------------+-----------+-------------+-----------+------------+ | 64836847 | Cultural_heritage_monuments_in_Darmstadt | 17 | 2 | 15 | 0 | +----------+------------------------------------------+-----------+-------------+-----------+------------+ While, in general, empty categories *do* show up in the result - as long as they have had a page in them in the past. So, as far as I can see, two things have to be addressed in a patch: 1) when a new page in category namespace is created, a row in the category table should be inserted 2) the category namespace should be scanned for missing entries in the category table, and those should be added.
Brad: Any chance you could take a look at it (or any idea who to ask instead)? Thanks in advance.
Merlijn's analysis is basically correct. I only have two things to add: 1. This is not limited to the API, it also applies to Special:Categories. See https://commons.wikimedia.org/wiki/Special:Categories/Cultural_heritage_monuments_in_Dari 2. This is actually the documented behavior, although I don't know whether that documentation exists outside of comments in maintenance/tables.sql: the definition of an existing category is that it at some point had a page in it, regardless of whether a corresponding page in namespace 14 exists or ever existed. The question is whether this is just bug 1 (improve the documentation) or if the definition of "category" should be changed as suggested. I see no particular reason not to change the definition besides "it's more work", but others might know more about the situation than I do.
(In reply to comment #2) > 2. This is actually the documented behavior Oh I see. Thanks for elaborating! Lowering priority.
To query all existing categories, it is possible to use allpages with apnamespace=14 But when a category contains at least one page and that page was removed, it will still be shown on allcategories, but can be filtered by acmin=1 (bug 26411)
Changing the definition sounds fine to me.
