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From Reuben Tonna <reub...@onvol.net>
Subject Lucene highlighter - issue - no highlights returned - a proposed solution
Date Thu, 04 Jan 2007 14:28:47 GMT
Hi,
    I am currently using the latest port of Lucene and Highlighter for 
an application that I am working on.  I found that the highlighting 
module was failing to return any highlight results, even if the term 
existed in the document.  After some investigaton the issue turns out to 
be in the file QueryTermExtractor.cs method GetTerms(..) reproduced 
below, with the changes necessary for the code to work correctly.

A couple of notes:

1. Iteration should be over the nonWeightedTerms hash.  I confirmed that 
this is what the Java version does.
2. Using the dictionary iteration over the hash.  Each iteration gives 
us access to the key or value.  Both are identical so I opted for the 
value (more readable) to get the term from.  Note that the original 
dictionary iteration will fail becauase an iterator cannot be casted to 
a Term type (only the value or key pointed to by the iterator can).

//fieldname MUST be interned prior to this call
        private static void  GetTerms(Query query, 
System.Collections.Hashtable terms, bool prohibited, System.String 
fieldName)
        {
            try
            {
                System.Collections.Hashtable nonWeightedTerms = new 
System.Collections.Hashtable();
                query.ExtractTerms(nonWeightedTerms);

                /*
                foreach (Term term in terms.Values)
                {
                    if ((fieldName == null) || (term.Field() == fieldName))
                    {
                        WeightedTerm temp = new 
WeightedTerm(query.GetBoost(), term.Text());
                        terms.Add(temp, temp);
                    }
                }
                */

                System.Collections.IDictionaryEnumerator iter = 
nonWeightedTerms.GetEnumerator();
                while (iter.MoveNext()) {
                    Term term = (Term)iter.Value;
                    if ((fieldName == null) || (term.Field() == 
fieldName)) {
                        WeightedTerm temp = new 
WeightedTerm(query.GetBoost(), term.Text());
                        terms.Add(temp, temp);
                    }
                }

                /*
                for (System.Collections.IEnumerator iter = 
nonWeightedTerms.GetEnumerator(); iter.MoveNext(); )
                {
                    Term term = (Term) iter.Current;
                    if ((fieldName == null) || (term.Field() == fieldName))
                    {
                        WeightedTerm temp = new 
WeightedTerm(query.GetBoost(), term.Text());
                        terms.Add(temp, temp);
                    }
                }
                 */
               
            }
            catch (System.NotSupportedException ignore)
            {
                //this is non-fatal for our purposes
            }
        }

Hth

Reuben.

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