Good day!
In my document, I have a date field, which contains ISO-8601 date, which can also be a period like "25-08-2016/P1D"
I want to search a document having exactly this date or period - so ,just having a same value of "date" field. Unfortunately, I was unable to do this. Tried different query strings, with escaping or without, like
date:"25-08-2016/P1D" - is transformed to PhraseQuery, which fails with
exception, AFAIUI since a field is just a String field
date:"25-08-2016/P1D" - same as above
date:25-08-2016/P1D -
does not fail with exception, but still PhraseQuery is created, and
nothing is being found
date:25-08-2016/P1D - parsing fails with "org.apache.lucene.queryparser.classic.TokenMgrError: Lexical error at line 1, column 150. Encountered: after : "/P1D"
What I'm doing wrong? How can I tell Lucene to search this field using simple string match, without any tokenization?
After some research I've got, that escaping query string is a wrong way - correct way to achieve this is customizing Query analyzer for necessary field ("date" in my case).
Map<String, Analyzer> analyzerPerField = new HashMap<String, Analyzer>();
analyzerPerField.put("date", new WhitespaceAnalyzer());
analyzer = new PerFieldAnalyzerWrapper(
new StandardAnalyzer(), analyzerPerField);
parser = new QueryParser("title", analyzer);
In given code, we just use WhitespaceAnalyzer (which is dividing query by whitespaces) instead of SimpleAnalyzer used by default, which is dividing text at non-letters. WhitespaceAnalyzer does not break ISO-8601 date.
For additional details about custom analyzing/tokenizing in lucene, please refer e.g. http://www.hascode.com/2014/07/lucene-by-example-specifying-analyzers-on-a-per-field-basis-and-writing-a-custom-analyzertokenizer/
Related
I'm using the SpanishAnalyzer class in Lucene 3.4. When I want to parse accented words, I'm having a strange result. If I parse, for example, these two words: "comunicación" and "comunicacion", the stems I'm getting are "comun" and "comunicacion". If I instead parse "maratón" and "maraton", I'm getting the same stem for both words ("maraton").
So, at least in my opinion, it's very strange that the same word, "comunicación", gives different results depending on it is accented or not. If I search the word "comunicacion", I should get the same result regardless of whether it's accented or not.
The code I'm using is the next one:
SpanishAnalyzer sa = new SpanishAnalzyer(Version.LUCENE_34);
QueryParser parser = new QueryParser(Version.LUCENE_34, "content", sa);
String str = "comunicación";
String str2 = "comunicacion";
System.out.println("first: " + parser.parse(str)); //stem = comun
System.out.println("second: " + parser.parse(str2)); //stem = comunicacion
The solution I've found to be able to get every single word that shares the stem of "comunicacion", accented or not, is to take off accents in a first step, and then parse it with the Analyzer, but I don't know if it's the right way.
Please, can anyone help me?
Did you check what tokenizer & tokenfilters SpanishAnalyzer uses? There is something called ASCIIFoldingFilter. Try placing it before the StemFilter. It will remove the accents
I'm extracting terms from the query calling ExtractTerms() on the Query object that I get as the result of QueryParser.Parse(). I get a HashTable, but each item present as:
Key - term:term
Value - term:term
Why are the key and the value the same? And more why is term value duplicated and separated by colon?
Do highlighters only insert tags or to do anything else? I want not only to get text fragments but to highlight the source text (it's big enough). I try to get terms and by offsets to insert tags by hand. But I worry if this is the right solution.
I think the answer to this question may help.
It is because .Net 2.0 doesnt have an equivalent to java's HashSet. The conversion to .Net uses Hashtables with the same value in key/value. The colon you see is just the result of Term.ToString(), a Term is a fieldname + the term text, your field name is probably "term".
To highlight an entire document using the Highlighter contrib, use the NullFragmenter
I want to find all documents in the index that have a certain field, regardless of the field's value. If at all possible using the query language, not the API.
Is there a way?
If you know the type of data stored in your field, you can try a range query. Per example, if your field contain string data, a query like field:[a* TO z*] would return all documents where there is a string value in that field.
I've done some experimenting, and it seems the simplest way to achieve this is to create a QueryParser and call SetAllowLeadingWildcard( true ) and search for field:* like so:
var qp = new QueryParser( Lucene.Net.Util.Version.LUCENE_29, field, analyzer );
qp.SetAllowLeadingWildcard( true );
var query = qp.Parse( "*" ) );
(Note I am setting the default field of the QueryParser to field in its constructor, hence the search for just "*" in Parse()).
I cannot vouch for how efficient this method is over other methods, but being the simplest method I can find, I would expect it to be at least as efficient as field:[* TO *], and it avoids having to do hackish things like field:[0* TO z*], which may not account for all possible values, such as values starting with non-alphanumeric characters.
Another solution is using a ConstantScoreQuery with a FieldValueFilter
new ConstantScoreQuery(new FieldValueFilter("field"))
Am using MultiFieldQueryParser for parsing strings like a.a., b.b., etc
But after parsing, its removing the dots in the string.
What am i missing here?
Thanks.
I'm not sure the MultiFieldQueryParser does what you think it does. Also...I'm not sure I know what you're trying to do.
I do know that with any query parser, strings like 'a.a.' and 'b.b.' will have the periods stripped out because, at least with the default Analyzer, all punctuation is treated as white space.
As far as the MultiFieldQueryParser goes, that's just a QueryParser that allows you to specify multiple default fields to search. So with the query
title:"Of Mice and Men" "John Steinbeck"
The string "John Steinbeck" will be looked for in all of your default fields whereas "Of Mice and Men" will only be searched for in the title field.
What analyzer is your parser using? If it's StopAnalyzer then the dot could be a stop word and is thus ignored. Same thing if it's StandardAnalyzer which cleans up input (includes removing dots).
(Repeating my answer from the dupe. One of these should be deleted).
The StandardAnalyzer specifically handles acronyms, and converts C.F.A. (for example) to cfa. This means you should be able to do the search, as long as you make sure you use the same analyzer for the indexing and for the query parsing.
I would suggest you run some more basic test cases to eliminate other factors. Try to user an ordinary QueryParser instead of a multi-field one.
Here's some code I wrote to play with the StandardAnalyzer:
StringReader testReader = new StringReader("C.F.A. C.F.A word");
StandardAnalyzer analyzer = new StandardAnalyzer();
TokenStream tokenStream = analyzer.tokenStream("title", testReader);
System.out.println(tokenStream.next());
System.out.println(tokenStream.next());
System.out.println(tokenStream.next());
The output for this, by the way was:
(cfa,0,6,type=<ACRONYM>)
(c.f.a,7,12,type=<HOST>)
(word,13,17,type=<ALPHANUM>)
Note, for example, that if the acronym doesn't end with a dot then the analyzer assumes it's an internet host name, so searching for "C.F.A" will not match "C.F.A." in the text.
I am using Lucene to allow a user to search for words in a large number of documents. Lucene seems to default to returning all documents containing any of the words entered.
Is it possible to change this behaviour? I know that '+' can be use to force a term to be included but I would like to make that the default action.
Ideally I would like functionality similar to Google's: '-' to exclude words and "abc xyz" to group words.
Just to clarify
I also thought of inserting '+' into all spaces in the query. I just wanted to avoid detecting grouped terms (brackets, quotes etc) and potentially breaking the query. Is there another approach?
This looks similar to the Lucene Sentence Search question. If you're interested, this is how I answered that question:
String defaultField = ...;
Analyzer analyzer = ...;
QueryParser queryParser = new QueryParser(defaultField, analyzer);
queryParser.setDefaultOperator(QueryParser.Operator.AND);
Query query = queryParser.parse("Searching is fun");
Like Adam said, there's no need to do anything to the query string. QueryParser's setDefaultOperator does exactly what you're asking for.
Why not just preparse the user search input and adjust it to fit your criteria using the Lucene query syntax before passing it on to Lucene. Alternatively, you could just create some help documentation on how to use the standard syntax to create a specific query and let the user decide how the query should be performed.
Lucene has a extensive query language as described here that describes everything you want except for + being the default but that's something you can simple handle by replacing spaces with +. So the only thing you need to do is define the format you want people to enter their search queries in (I would strongly advise to adhere to the default Lucene syntax) and then you can write the transformations from your own syntax to the Lucene syntax.
The behavior is hard-coded in method addClause(List, int, int, Query) of class org.apache.lucene.queryParser.QueryParser, so the only way to change the behavior (other than the workarounds above) is to change that method. The end of the method looks like this:
if (required && !prohibited)
clauses.addElement(new BooleanClause(q, BooleanClause.Occur.MUST));
else if (!required && !prohibited)
clauses.addElement(new BooleanClause(q, BooleanClause.Occur.SHOULD));
else if (!required && prohibited)
clauses.addElement(new BooleanClause(q, BooleanClause.Occur.MUST_NOT));
else
throw new RuntimeException("Clause cannot be both required and prohibited");
Changing "SHOULD" to "MUST" should make clauses (e.g. words) required by default.