[LUCENE-1518] Merge Query and Filter classes

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4
• Fix Version/s: 5.1, 6.0
• Component/s: core/search
• Lucene Fields: New, Patch Available
• Assignee: Unassigned
• Reporter: Uwe Schindler
• Created: 12/Jan/09 19:44
• Updated: 28/Aug/22 11:57
• Resolved: 13/Feb/15 17:12

Description

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.

Issue Links

• is part of: LUCENE-1345 Allow Filter as clause to BooleanQuery