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https://issues.apache.org/jira/browse/LUCENE-2868?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12981774#action_12981774
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Earwin Burrfoot commented on LUCENE-2868:
-----------------------------------------
We here use an intermediate query AST, with a number of walkers that do synonym
substitution, optimization, caching, rewriting for multiple fields, and finally
- generating a tree of Lucene Queries.
I can share a generic reflection-based visitor that's somewhat more handy than
default visitor pattern in java.
Usage looks roughly like:
{code}
class ToStringWalker extends DispatchingVisitor<String> { // String here stands
for the type of walk result
String visit(TermQuery q) {
return "{term: " + q.getTerm() + "}";
}
String visit(BooleanQuery q) {
StringBuffer buf = new StringBuffer();
buf.append("{boolean: ");
for (BooleanQuery.Clause clause: q.clauses()) {
buf.append(dispatch(clause.getQuery()).append(", "); // Here we
}
buf.append("}");
return buf.toString();
}
String visit(SpanQuery q) { // Runs for all SpanQueries
.....
}
String visit(Query q) { // Runs for all Queries not covered by a more exact
visit() method
......
}
}
Query query = ...;
String stringRepresentation = new ToStringWalker().dispatch(query);
{code}
dispatch() checks its parameter runtime type, picks a visit()'s most close
overload (according to java rules for compile-time overloaded method
resolution), and invokes it.
> It should be easy to make use of TermState; rewritten queries should be
> shared automatically
> --------------------------------------------------------------------------------------------
>
> Key: LUCENE-2868
> URL: https://issues.apache.org/jira/browse/LUCENE-2868
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Query/Scoring
> Reporter: Karl Wright
> Attachments: query-rewriter.patch
>
>
> When you have the same query in a query hierarchy multiple times, tremendous
> savings can now be had if the user knows enough to share the rewritten
> queries in the hierarchy, due to the TermState addition. But this is clumsy
> and requires a lot of coding by the user to take advantage of. Lucene should
> be smart enough to share the rewritten queries automatically.
> This can be most readily (and powerfully) done by introducing a new method to
> Query.java:
> Query rewriteUsingCache(IndexReader indexReader)
> ... and including a caching implementation right in Query.java which would
> then work for all. Of course, all callers would want to use this new method
> rather than the current rewrite().
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