This looks like a bug - can you open a JIRA ticket?
Alan Woodward
www.flax.co.uk
On 13 May 2016, at 22:33, Daniel Bigham wrote:
> I am experimenting with supporting synonyms on the query side by doing query
> expansion.
>
> For example, the query "open webpage" can be expanded if the following things
> are synonyms:
>
> "open" | "go to"
>
> This becomes the following: (I'm using both the stop word filter and the
> stemming filter)
>
> spanNear(
> [
> spanOr([Title:open, Title:go]),
> Title:webpag
> ],
> 0,
> true
> )
>
> Notice that "go to" became just "go", because apparently "to" is removed by
> the stop word filter.
>
> Interestingly, if you turn "go to webpage" into a phrase, you get "go ?
> webpage", but if you turn "go to" into a phrase, you just get "go", because
> apparently a trailing stop word in a PhraseQuery gets dropped. (there would
> actually be no way to represent the gap currently because it represents gaps
> implicitly via the position of the phrase tokens, and if there is no second
> token, there's no way to implicitly indicate that there is a gap there)
>
> The above query then fails to match "go to webpage", because "go to webpage"
> in the index tokenizes as "go _ webpage", and the query, because it lost its
> gap, tried to only match "go webpage".
>
> To try and work around that, I represent "go to" not as a phrase, but as a
> SpanNearQuery, like this:
>
> spanNear(
> [
> spanOr(
> [
> Title:open,
> spanNear([Title:go, SpanGap(:1)], 0, true),
> ]
> ),
> Title:webpag
> ],
> 0,
> true
> )
>
> However, when I run that query, I get the following:
>
> A Java exception occurred: java.lang.UnsupportedOperationException
> at
> org.apache.lucene.search.spans.SpanNearQuery$GapSpans.positionsCost(SpanNearQuery.java:398)
> at
> org.apache.lucene.search.spans.ConjunctionSpans.asTwoPhaseIterator(ConjunctionSpans.java:96)
> at
> org.apache.lucene.search.spans.NearSpansOrdered.asTwoPhaseIterator(NearSpansOrdered.java:45)
> at
> org.apache.lucene.search.spans.ScoringWrapperSpans.asTwoPhaseIterator(ScoringWrapperSpans.java:88)
> at
> org.apache.lucene.search.ConjunctionDISI.addSpans(ConjunctionDISI.java:104)
> at
> org.apache.lucene.search.ConjunctionDISI.intersectSpans(ConjunctionDISI.java:82)
> at
> org.apache.lucene.search.spans.ConjunctionSpans.<init>(ConjunctionSpans.java:41)
> at
> org.apache.lucene.search.spans.NearSpansOrdered.<init>(NearSpansOrdered.java:54)
> at
> org.apache.lucene.search.spans.SpanNearQuery$SpanNearWeight.getSpans(SpanNearQuery.java:232)
> at org.apache.lucene.search.spans.SpanWeight.scorer(SpanWeight.java:134)
> at org.apache.lucene.search.spans.SpanWeight.scorer(SpanWeight.java:38)
> at org.apache.lucene.search.Weight.bulkScorer(Weight.java:135)
>
> ... and when I look up that GapSpans class in SpanNearQuery.java, I see:
>
> @Override
> public float positionsCost() {
> throw new UnsupportedOperationException();
> }
>
> Does this UnsupportedOperationException imply that "we haven't implemented
> that yet"? Or does it imply "you're doing something wrong"?
>
> If I'm doing something wrong, any idea what it might be?
>
> Thanks,
> Daniel
>
>
>
>
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