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From "Luis Alves (JIRA)" <>
Subject [jira] Commented: (LUCENE-2039) Regex support and beyond in JavaCC QueryParser
Date Thu, 12 Nov 2009 20:20:39 GMT


Luis Alves commented on LUCENE-2039:

Simon and Adriano,
Can you comment on the example below.


regexp:title:"/blah[a-z]+[0-9]+/"  <- regexp extension, title index field
complex_phrase:title:"(sun OR sunny) sky" <- complex_phrase extension, title index field

regexp_phrase::"/blah[a-z]+[0-9]+/"  <- regexp extension, default field
complex_phrase::"(sun OR sunny) sky" <- complex_phrase extension, default field

title:"blah" <- regular field query

This would allow the filedname and phrases or terms to be passed to a extension, and still
be very compatible with the old syntax.
(only double quotes and backslash need to be escaped in a phrase, so it should cover a big
number of future extensions)

Something like this would work for base64, but it would be target at programmatic layer, since
users will not be able to generate that base64 strings, and it is supported by the syntax
described above.



For extensions that won't work well with escaping double quotes and back-slash, we probably
need some other delimiter, probably more than a single character
some sugestions below:
xml style:
1) xpath:xmlfield:<[[ //title[@lang="c:\windowspath\folder" ]]>
2) xpath:xmlfield:<![CDATA[ //title[@lang="c:\windowspath\folder" ]]>

another one
3) xpath:xmlfield:\![CDATA[ //title[@lang="c:\windowspath\folder" ]]!


Any of the sequences above is good OK with me. 
This should not affect old queries very much since the new syntax tokens would be 
":<[[ "  and "]]>" and these shouldn't be common on any lucene queries.
Still not very user friendly, but better than the base64 approach.

> Regex support and beyond in JavaCC QueryParser
> ----------------------------------------------
>                 Key: LUCENE-2039
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: QueryParser
>            Reporter: Simon Willnauer
>            Assignee: Grant Ingersoll
>            Priority: Minor
>             Fix For: 3.1
>         Attachments: LUCENE-2039.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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