[Wikidata-bugs] [Maniphest] [Created] T170196: Categorymembers: Join on redirect items causes results to explode.

[famewi]

famewi created this task. famewi added a project: Wikidata-Query-Service. Herald added a subscriber: Aklapper. Herald added projects: Wikidata, Discovery.

TASK DESCRIPTION

When joining on category items that are redirects, an invalid result set will be produced: Every item in the original result set will be combined with every item in the second graph.

Steps to reproduce:

1. Use the categorymembers generator to perform a query on a category that contains at least one redirect. Ensure that the redirect item is part of the result set.
2. Add a second graph to filter down the result set.

Expected result: Only the items that match both graphs are returned.
Actual result: In the result, every item of the first graph gets combined with every item of the second graph.

Example query:

SELECT *
WHERE {
  SERVICE wikibase:mwapi {
	 bd:serviceParam wikibase:api "Generator" .
     bd:serviceParam wikibase:endpoint "en.wikipedia.org" .
     bd:serviceParam mwapi:gcmpageid "24904747" .
     bd:serviceParam mwapi:generator "categorymembers" .
     bd:serviceParam mwapi:gcmprop "title" .

     # Here item 2 is a redirect. Lowering the limit to 1 will again produce the expected result.
     bd:serviceParam mwapi:gcmlimit "2" .

    ?title wikibase:apiOutputItem mwapi:title . 
    ?item wikibase:apiOutputItem mwapi:item .
  }
  ?item wdt:P625 ?location
}

Test data:

• https://en.wikipedia.org/wiki/Category:Monuments_to_composers (Q8640743)
  • Page ID: 29118741
  • Redirect: item 1 of 16
• https://en.wikipedia.org/wiki/Category:Obelisks_in_Canada (Q8691068)
  • Page ID: 24904747
  • Redirect: item 2 of 3
  • Prepared query: http://tinyurl.com/y8js6upb
• https://en.wikipedia.org/wiki/Category:Obelisks_in_the_United_States (Q8691091)
  • Page ID: 14498651
  • item 21 of 38

TASK DETAIL

https://phabricator.wikimedia.org/T170196

EMAIL PREFERENCES

https://phabricator.wikimedia.org/settings/panel/emailpreferences/

To: famewi
Cc: Wikidata, famewi, Aklapper, GoranSMilovanovic, QZanden, EBjune, merbst, Avner, debt, Gehel, Jonas, FloNight, Xmlizer, Izno, jkroll, Smalyshev, Wikidata-bugs, Jdouglas, aude, Tobias1984, Manybubbles, Mbch331

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