[LUCENE-344] [PATCH] Introduction of QueryFactory interface for Query construction

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Not A Problem
• Component/s: core/queryparser

Environment

Operating System: Linux
Platform: Other

• Bugzilla Id: 33449
• Assignee: Unassigned
• Reporter: Matthew Denner
• Created: 09/Feb/05 03:58
• Updated: 28/Aug/22 11:20
• Resolved: 26/Jan/11 08:33

Description

To override the default behaviour of the QueryParser you must currently extend
it and override the appropriate methods. This seemed to be a little awkward.

To enable a (hopefully) more flexible means of creating Query instances it
would seem better to introduce a QueryFactory interface and pass an instance of
an implementation of this interface to the QueryParser, having the QueryParser
callback to it to construct the query as it parses it. With this design you
could write something like:

QueryParser parser = new QueryParser("defaultField", new StandardAnalyzer(),
new QueryFactoryImpl());

Where 'QueryFactoryImpl' is an implementation of the QueryFactory interface.
If you wanted to add the ability to lower case all of your queries you could
then write:

QueryParser parser = new QueryParser("defaultField", new StandardAnalyzer(),
new LowerCaseQueryFactory(new QueryFactoryImpl()));

Where 'LowerCaseQueryFactory' is a decorator around another QueryFactory
instance and it simply lowercases all the terms passed to it before delegating
the actual query construction. This is a simple example, but more powerful
functionality could be added not by changing the QueryParser, but by creating a
new QueryFactory implementation.

I have a patch for this which will be forthcoming in a moment.

Issue Links

• is duplicated by: LUCENE-1061 Adding a factory to QueryParser to instantiate query instances