[JENA-954] OpAsQuery can move sub-query modifiers onto outer query

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Jena 2.13.0
• Fix Version/s: Jena 3.0.0
• Component/s: ARQ
• Assignee: Rob Vesse
• Reporter: Rob Vesse
• Created: 04/Jun/15 11:27
• Updated: 29/Jul/15 14:52
• Resolved: 04/Jun/15 13:39

Description

Reported on the mailing list:

http://s.apache.org/jena-algebra-roundtripping-bug

Some queries roundtrip incorrectly through the Algebra.compile() to OpAsQuery.asQuery() flow e.g.

SELECT (COUNT(*) as ?count) {
  SELECT DISTINCT ?uri ?graph WHERE {
    GRAPH ?graph {
      ?uri ?p ?o .
      }
    } LIMIT 1
}

Produces algebra:

project (?tripod_count_var)
  (extend ((?tripod_count_var ?.0))
    (group () ((?.0 (count)))
      (distinct
        (project (?uri ?graph)
          (graph ?graph
            (bgp (triple ?uri ?p ?o))))))))

Which round trips back to:

SELECT DISTINCT  (count(*) AS ?tripod_count_var)
WHERE
  { { SELECT  ?uri ?graph
      WHERE
        { GRAPH ?graph
            { ?uri ?p ?o}
        }
    }
  }

Note that the DISTINCT was incorrectly moved to the outer query

The problem is that the conversion does not correct cope with the case of being within a project and needs to spawn a sub-converter to cope as OpProject already does