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From Chris Hostetter <hossman_luc...@fucit.org>
Subject Re: Using NOT queries inside parentheses
Date Mon, 06 Mar 2006 19:03:49 GMT

: The following query does not work as expected for me:
: "alwaysTrueField:true (-name:john)"
: neither does this:
: "alwaysTrueField:true +(-name:john)"

: Does lucene run a sub-query for each part of the query inside
: parentheses, which is why the NOT query that is alone doesn't work? I am

Basically yes, the parens force the creation of a BooleanQuery, which is
invalid since it only contains prohited clauses.

: Any suggestions on how to work around this (buggy?) behaviour?

I use the following (1.4.3) method to deal with situations like this...

    /**
     * tests a BooleanQuery to see if it is directly usable, meaning it
     * has at least one clause that is not prohibited.
     *
     * @param bq a BooleanQuery to test
     * @returns false if bq null or contains all prohibited items, else true
     */
    public static boolean usableBooleanQuery(BooleanQuery bq) {
        if (null == bq) {
            return false;
        }

        /* if we find *1* clause that's not prohibited, return true */
        BooleanClause[] clauses = bq.getClauses();
        for (int c = 0; clauses != null && c < clauses.length; c++) {
            if (! clauses[c].prohibited) {
                return true;
            }
        }
        return false;
    }

It can be used something like this...

   Query at = new TermQuery(new Term("alwaysTrueField","true));
   Query user = queryParser.parse(userInput);
   if (user instanceof BooleanQuery) {
      BooleanQuery bq = (BooleanQuery)user;
      if (! usableBooleanQuery(bq)) {
         bq.add(at, true, false); /* add 'always true' clause directly */
         return bq;
      }
   }
   /* if we made it here, wrape both clauses.
   BooleanQuery q = new BooleanQuery();
   q.add(at, true, false);
   q.add(user, true, false);
   return q;


(i think that's right, the specific cases where i use it are more
complicated so i can't cut/paste ... but i'm pretty sure the logic is
correct in that example, you should write some unit tests to be sure
before you do something like this.)

-Hoss


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