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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1518) Merge Query and Filter classes
Date Tue, 10 Feb 2009 07:54:59 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12672199#action_12672199
] 

Uwe Schindler commented on LUCENE-1518:
---------------------------------------

This patch does not want to completely merge queries and filters. It only gives the possibility
to use a Filter directly as a query. So ValueSourceQuery will stay direct subclass of Query
and not of Filter and can be used as scorer only. I think completely merging both is not a
good idea.

But for easy usage, the idea of making filter automatically work as query (using a constant
score algorithm) may be good. So queries (e.g. without matching, also conventional queries)
 can stay alive, but filters can be used as query (and BooleanQuery could automatically have
filters as clauses, and is able to optimize and factor away scoring). The user only has a
easy understandable API and would not be affected by thinking about ("is it better to use
a ConstantScoreQuery or should I just filter the results other boolean query clauses?").

> Merge Query and Filter classes
> ------------------------------
>
>                 Key: LUCENE-1518
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1518
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>    Affects Versions: 2.4
>            Reporter: Uwe Schindler
>         Attachments: LUCENE-1518.patch
>
>
> This issue presents a patch, that merges Queries and Filters in a way, that the new Filter
class extends Query. This would make it possible, to use every filter as a query.
> The new abstract filter class would contain all methods of ConstantScoreQuery, deprecate
ConstantScoreQuery. If somebody implements the Filter's getDocIdSet()/bits() methods he has
nothing more to do, he could just use the filter as a normal query.
> I do not want to completely convert Filters to ConstantScoreQueries. The idea is to combine
Queries and Filters in such a way, that every Filter can automatically be used at all places
where a Query can be used (e.g. also alone a search query without any other constraint). For
that, the abstract Query methods must be implemented and return a "default" weight for Filters
which is the current ConstantScore Logic. If the filter is used as a real filter (where the
API wants a Filter), the getDocIdSet part could be directly used, the weight is useless (as
it is currently, too). The constant score default implementation is only used when the Filter
is used as a Query (e.g. as direct parameter to Searcher.search()). For the special case of
BooleanQueries combining Filters and Queries the idea is, to optimize the BooleanQuery logic
in such a way, that it detects if a BooleanClause is a Filter (using instanceof) and then
directly uses the Filter API and not take the burden of the ConstantScoreQuery (see LUCENE-1345).
> Here some ideas how to implement Searcher.search() with Query and Filter:
> - User runs Searcher.search() using a Filter as the only parameter. As every Filter is
also a ConstantScoreQuery, the query can be executed and returns score 1.0 for all matching
documents.
> - User runs Searcher.search() using a Query as the only parameter: No change, all is
the same as before
> - User runs Searcher.search() using a BooleanQuery as parameter: If the BooleanQuery
does not contain a Query that is subclass of Filter (the new Filter) everything as usual.
If the BooleanQuery only contains exactly one Filter and nothing else the Filter is used as
a constant score query. If BooleanQuery contains clauses with Queries and Filters the new
algorithm could be used: The queries are executed and the results filtered with the filters.
> For the user this has the main advantage: That he can construct his query using a simplified
API without thinking about Filters oder Queries, you can just combine clauses together. The
scorer/weight logic then identifies the cases to use the filter or the query weight API. Just
like the query optimizer of a RDB.

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