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
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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