Michael and Forum,-
This is amazing, thanks.
i will try both cases.
i can also have "term1 term2Char1term2Char2*"
and so on with term2's next chars.
I hope the latest version on github for this
class works with Lucene Version 7.7.2.
Best regards
> On Feb 18, 2020, at 8:33 PM, Michael Froh <msf...@gmail.com> wrote:
>
>
> In your example, it looks like you wanted the second term to match based on
> the first character, or prefix, of the term.
>
> While you could use a WildcardQuery with a term value of "term2FirstChar*",
> PrefixQuery seemed like the simpler approach. WildcardQuery can handle more
> general cases, like if you want to match on something like "a*b*c".
>
> Technically, the PrefixQuery compiles down to a slightly simpler automaton,
> but I only figured that out by writing a simple unit test:
>
> public void testAutomata() {
> Automaton prefixAutomaton = PrefixQuery.toAutomaton(new
> BytesRef("a"));
> Automaton wildcardAutomaton = WildcardQuery.toAutomaton(new
> Term("foo", "a*"));
>
> System.out.println("PrefixQuery(\"a\")");
> System.out.println(prefixAutomaton.toDot());
> System.out.println("WildcardQuery(\"a*\")");
> System.out.println(wildcardAutomaton.toDot());
> }
>
> That produces the following output:
>
> PrefixQuery("a")
> digraph Automaton {
> rankdir = LR
> node [width=0.2, height=0.2, fontsize=8]
> initial [shape=plaintext,label=""]
> initial -> 0
> 0 [shape=circle,label="0"]
> 0 -> 1 [label="a"]
> 1 [shape=doublecircle,label="1"]
> 1 -> 1 [label="\\U00000000-\\U000000ff"]
> }
> WildcardQuery("a*")
> digraph Automaton {
> rankdir = LR
> node [width=0.2, height=0.2, fontsize=8]
> initial [shape=plaintext,label=""]
> initial -> 0
> 0 [shape=circle,label="0"]
> 0 -> 1 [label="a"]
> 1 [shape=doublecircle,label="1"]
> 1 -> 2 [label="\\U00000000-\\U0010ffff"]
> 2 [shape=doublecircle,label="2"]
> 2 -> 2 [label="\\U00000000-\\U0010ffff"]
> }
>
>
>
>> On Tue, 18 Feb 2020 at 13:52, <baris.ka...@oracle.com> wrote:
>> Michael and Forum,-
>> Thanks for thegreat explanations.
>>
>> one question please:
>>
>> why is PrefixQuery used instead of WildCardQuery in the below snippet?
>>
>> Best regards
>>
>> > On Feb 17, 2020, at 3:01 PM, Michael Froh <msf...@gmail.com> wrote:
>> >
>> > Hi Baris,
>> >
>> > The idea with PhraseWildcardQuery is that you can mix literal "exact" terms
>> > with "MultiTerms" (i.e. any subclass of MultiTermQuery). Using addTerm is
>> > for exact terms, while addMultiTerm is for things that may match a number
>> > of possible terms in the given position.
>> >
>> > If you want to search for term1 followed by any term that starts with a
>> > given character, I would suggest using:
>> >
>> > int maxMultiTermExpansions = ...; // Discussed below
>> > PhraseWildCardQuery.Builder builder = new PhraseWildcardQuery("field",
>> > maxMultiTermExpansions);
>> > builder.addTerm(new BytesRef("term1")); // Add fixed term in position 0
>> > builder.addMultiTerm(new PrefixQuery(new Term("field", "term2FirstChar")));
>> > // Add multiterm in position 1
>> > Query q = builder.build();
>> >
>> > The PrefixQuery effectively gets expanded into a bunch of possible terms,
>> > based on the term dictionary on each index segment. To avoid expanding to
>> > cover too many terms (say, if you added a bunch of WildcardQuery),
>> > maxMultiTermExpansions serves as a guard rail, to put a rough bound on
>> > memory consumption and query execution time. If you're interested in
>> > details of how the maxMultiTermExpansions budget is distributed across
>> > MultiTerms, check out PhraseWildcardQuery.createWeight. If you're just
>> > running an experiment in your IDE, you could probably set
>> > maxMultiTermExpansions to Integer.MAX_VALUE. (If you're running in a
>> > production environment, it's likely a good idea to tune it down based on
>> > your memory/latency constraints.)
>> >
>> > Incidentally, for tracking down the source code for anything in Lucene,
>> > it's probably better to go to GitHub for the most up-to-date source:
>> > https://urldefense.com/v3/__https://github.com/apache/lucene-solr/blob/master/lucene/sandbox/src/java/org/apache/lucene/search/PhraseWildcardQuery.java__;!!GqivPVa7Brio!ONqQgLIltNBUuSo5Cn_Fz7-wuR1LQv68YS_z-6g7X-S86PHQtT9tKl7VbIq9tVLYyw$
>> >
>> > .
>> >
>> > Hope that helps,
>> > Michael
>> >
>> >> On Thu, 13 Feb 2020 at 12:29, <baris.ka...@oracle.com> wrote:
>> >>
>> >> Hi,-
>> >>
>> >> i hope everyone is doing great.
>> >>
>> >> if i want to do the following search with PhraseWildCardQuery and
>> >> thanks to this forum for letting me know about this class (Especially to
>> >> David and Bruno)
>> >>
>> >> term1 term2FirstChar*
>> >>
>> >> i need to do two ways: (i found the source code at
>> >>
>> >> https://urldefense.com/v3/__https://fossies.org/linux/lucene/sandbox/src/java/org/apache/lucene/search/PhraseWildcardQuery.java__;!!GqivPVa7Brio!ONqQgLIltNBUuSo5Cn_Fz7-wuR1LQv68YS_z-6g7X-S86PHQtT9tKl7VbIpV8n29nQ$
>> >>
>> >> )
>> >>
>> >> /*
>> >>
>> >> maxMultiTermExpansions - The maximum number of expansions across all
>> >> multi-terms and across all segments. It counts expansions for each
>> >> segments individually, that allows optimizations per segment and unused
>> >> expansions are credited to next segments. This is different from
>> >> MultiPhraseQuery and SpanMultiTermQueryWrapper which have an expansion
>> >> limit per multi-term.
>> >>
>> >> segmentOptimizationEnabled - Whether to enable the segment optimization
>> >> which consists in ignoring a segment for further analysis as soon as a
>> >> term is not present inside it. This optimizes the query execution
>> >> performance but changes the scoring. The result ranking is preserved.
>> >>
>> >> */
>> >>
>> >>
>> >> 1st way:
>> >>
>> >> PhraseWildCardQuery.Builder builder = PharseWildCardQuery.Builder(field,
>> >> 2 _*/<<< i dont know what number to use here for
>> >> maxMultiTermExpansions>>>/*_, true/*boolean segmentOptimizationEnabled*/)
>> >>
>> >> pwcqBuilder.addTerm(field, new Term(field, "term1"));
>> >>
>> >> pwcqBuilder.addTerm(field,new Term(field, "term2FirstChar"));
>> >>
>> >> PhraseWildCardQuery pwcq = pwcqBuilder.build();
>> >>
>> >> or
>> >>
>> >> 2nd way:
>> >>
>> >> pwcqBuilder.addMultiTerm(MultiTermQuery object here contaning {field,
>> >> "term1"} and {field ,"term2FirstChar"});
>> >>
>> >> PhraseWildCardQuery pwcq = pwcqBuilder.build();
>> >>
>> >>
>> >> Then this pwcq object will be fed into IndexSearcher's as the query
>> >> parameter.
>> >>
>> >>
>> >> Now, it looks like the first way will not consider expansions or in
>> >> other words wildcard? Am i right?
>> >>
>> >> i also need to understand this maxMultiTermExpansions parameter better.
>> >> For instance if first way is used, will maxMultiTermExpansions be
>> >> meaningful?
>> >>
>> >>
>> >> Thanks
>> >>
>> >>
>>
>>
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