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https://issues.apache.org/jira/browse/LUCENE-1518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12704609#action_12704609
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Paul Elschot edited comment on LUCENE-1518 at 4/30/09 5:30 AM:
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bq. Create a FilterWeight which wraps a Filter and provide a Scorer
implementation with a constant score. (This does not handle the "no scoring"
mode, unless "no scoring" can be achieved with score=0.0f, while constant is
any other value, defaulting to 1.0f).
The current patch at LUCENE-1345 does not need such a FilterWeight; the no
scoring case is handled by not asking for score values.
Using score=0.0f for no scoring might not work for BooleanQuery because it also
has a coordination factor that depends on the number of matching query clauses.
The patch at 1345 does not change that coordination factor for backward
compatibility, even though the coordination factor might also depend on the
number of a matching filter clauses.
was (Author: paul.elsc...@xs4all.nl):
bq. Create a FilterWeight which wraps a Filter and provide a Scorer
implementation with a constant score. (This does not handle the "no scoring"
mode, unless "no scoring" can be achieved with score=0.0f, while constant is
any other value, defaulting to 1.0f).
The current patch at LUCENE-1345 does not need such a FilterWeight; the no
scoring case is handled by not asking for score values.
Using score=0.0f for no scoring might not work for BooleanQuery because it also
has a coordination factor that depends on the number of matching queries
clauses. The patch at 1345 does not change that coordination factor for
backward compatibility, even though the coordination factor might also depend
on the number of a matching filter 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
> Fix For: 2.9
>
> 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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