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https://issues.apache.org/jira/browse/LUCENE-2039?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12790223#action_12790223
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David Kaelbling commented on LUCENE-2039:
-----------------------------------------
> David here is an example of what I mean by wrapping the top level parser.
> This would give
> you access to all the settings right away inside your extension.
Maybe I'm oversimplifying. As a lazy implementor I want to write something
like this:
ext.add("regex", new ParserExtension() {
public Query parse(ExtensionQuery q) throws ParseException {
return new RegexQuery(new Term(q.getField(), q.getRawQueryString()));
} } );
My ParserExtension can query any top level parser settings it likes, but how do
I get those
values down into RegexQuery? Or whatever full parser I'm invoking?
> Regex support and beyond in JavaCC QueryParser
> ----------------------------------------------
>
> Key: LUCENE-2039
> URL: https://issues.apache.org/jira/browse/LUCENE-2039
> Project: Lucene - Java
> Issue Type: Improvement
> Components: QueryParser
> Reporter: Simon Willnauer
> Assignee: Simon Willnauer
> Priority: Minor
> Fix For: 3.1
>
> Attachments: LUCENE-2039.patch, LUCENE-2039_field_ext.patch,
> LUCENE-2039_field_ext.patch, LUCENE-2039_field_ext.patch,
> LUCENE-2039_field_ext.patch, LUCENE-2039_field_ext.patch,
> LUCENE-2039_wrap_master_parser.patch
>
>
> Since the early days the standard query parser was limited to the queries
> living in core, adding other queries or extending the parser in any way
> always forced people to change the grammar file and regenerate. Even if you
> change the grammar you have to be extremely careful how you modify the parser
> so that other parts of the standard parser are affected by customisation
> changes. Eventually you had to live with all the limitation the current
> parser has like tokenizing on whitespaces before a tokenizer / analyzer has
> the chance to look at the tokens.
> I was thinking about how to overcome the limitation and add regex support to
> the query parser without introducing any dependency to core. I added a new
> special character that basically prevents the parser from interpreting any of
> the characters enclosed in the new special characters. I choose the forward
> slash '/' as the delimiter so that everything in between two forward slashes
> is basically escaped and ignored by the parser. All chars embedded within
> forward slashes are treated as one token even if it contains other special
> chars like * []?{} or whitespaces. This token is subsequently passed to a
> pluggable "parser extension" with builds a query from the embedded string. I
> do not interpret the embedded string in any way but leave all the subsequent
> work to the parser extension. Such an extension could be another full
> featured query parser itself or simply a ctor call for regex query. The
> interface remains quiet simple but makes the parser extendible in an easy way
> compared to modifying the javaCC sources.
> The downsides of this patch is clearly that I introduce a new special char
> into the syntax but I guess that would not be that much of a deal as it is
> reflected in the escape method though. It would truly be nice to have more
> than once extension an have this even more flexible so treat this patch as a
> kickoff though.
> Another way of solving the problem with RegexQuery would be to move the JDK
> version of regex into the core and simply have another method like:
> {code}
> protected Query newRegexQuery(Term t) {
> ...
> }
> {code}
> which I would like better as it would be more consistent with the idea of the
> query parser to be a very strict and defined parser.
> I will upload a patch in a second which implements the extension based
> approach I guess I will add a second patch with regex in core soon too.
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