Discussion at Wikidata:Project_chat related to this issue.

The lack of powerful means to traverse the Wikidata knowledge tree within Lua modules is in fact a problem for Wikidata as well, not only for module coders on Wikipedia side. {{#property:}}/{{#statement:}} parser functions and Module:Wikidata allow simple data retrieval from the connected item, but any lookup of items (as indicated by Jarekt) is very difficult. Users deal with this problem by adding all information they want to access from a client (e.g. in an infobox) directly to the connected item—even if it is utterly misplaced there (for instance country qualifiers to place of birth data in an item about a person).

The most effective method to search in the Wikidata knowledge tree is likely a SPARQL query. It would thus be very useful if a SPARQL interface for item lookup was available in Lua.

Yeah totally. We "just" need to figure out how to make this work without killing the site.

At least in eswiki we would also need a way to check if an entity or a value are from a given type (or list of types). For us it would be very useful having a way to do queries like this through Lua:

ASK {
  BIND(wd:Q6012487 AS ?item)
  VALUES ?class { wd:Q386724 }
  ?item wdt:P31/wdt:P279* ?class. hint:Prior hint:gearing "forward".
}

Which would be called with some lua function call like mw.wikibase.checkEntityType( id, { typeId1, typeId2,... }) which would return true or false depending on the response of the query. @Lydia_Pintscher, as this is already done for the constraint check API would it be possible implementing something like this for Lua too without killing the site? Having this would simplify our transition to a single infobox template.

This use case was marked as duplicate of this task and merged into it, but I think the use case we need in eswiki is simpler to implement and that it's not the same as the one in this task.

Part of this sounds like T179155: Find a better solution for dewiki's Modul:Wikidata isParent.