[jira] [Commented] (LUCENE-1518) Merge Query and Filter classes

["Uwe Schindler (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-1518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14316785#comment-14316785 ] 

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

Long time ago :-)

So this looks fine, makes it easy to use Filters as real queries. There is only one thing: The score returned is now always be 0. If you want to get the old behaviour where you get the boost as score, you just have to wrap the Filter with ConstantScoreQuery, like it was before?

There is a typo in description of Filter: "Convenient base class for building queries that only perform matching, but no scoring. The scorer produced by such queries always returns 0." - i think it should be "returns 0 as score".

One other thing: QueryWrapperFilter is now obsolete, or not?

So looks really fine.

> Merge Query and Filter classes
> ------------------------------
>
>                 Key: LUCENE-1518
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1518
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/search
>    Affects Versions: 2.4
>            Reporter: Uwe Schindler
>             Fix For: 4.9, Trunk
>
>         Attachments: LUCENE-1518.patch, 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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