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Date: Mon, 30 Nov 2009 09:27:19 +1100
Message-ID: <bb132a4a0911291427g410fd5demd7ef08d51088509f@mail.gmail.com>
Subject: New Query Parser: converting a QueryNode back into a String?
From: Daniel Noll <daniel@nuix.com>
To: java-user@lucene.apache.org
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Hi all.

I've been playing a lot with the new query parser framework, primarily
as a means of converting a query structure back into a string.  I was
hoping that I would be able to use it for the parsing direction as
well a bit later, to simply our customisations on the older query
parser, and that much certainly does seem possible.

But I've noticed what might be some strange behaviour with range
queries, specifically with what happens when I try to convert them
back into the original query string.

        StandardQueryParser queryParser = new StandardQueryParser();
        QueryNode node = queryParser.getSyntaxParser().parse("size:[0
TO 1000]", null);
        System.out.println(node.toString());

Prints this:

    <parametricRange>
        <parametric field='size' operator='<=' text='1000'/>
        <parametric field='size' operator='>=' text='0'/>
    </parametricRange>

And this is fine (though the order of the inner elements is
surprising), but this:

        System.out.println(node.toQueryString(new EscapeQuerySyntaxImpl()));

Prints this:

    size>="0" AND size<="1000"

This is nothing like the original query string passed in, and on top
of that, if you parse it a second time through the same query parser,
you get something completely new again, showing that the parser itself
doesn't understand this syntax:

<boolean operation='default'>
<field start='1' end='6' field='null' text='size>='/>
<boolean operation='and'>
<quotedfield start='8' end='8' field='null' term='0'/>
<field start='15' end='20' field='null' text='size<='/>
</boolean>
<quotedfield start='22' end='25' field='null' term='1000'/>
</boolean>

So what I would like to know is:

1. What is the simplest way for me to have a range query which I can
convert back into the original string?

2. Is the current model of the new query parser going to work for
everyone?  I had a bit of a think about this and it would seem that as
soon as someone defines a new SyntaxParser which uses a completely
different format, the QueryNode objects which come out would no longer
know how to convert themselves back into that original syntax.  It
would seem that Lucene would also need a corresponding SyntaxFormatter
to convert from QueryNode back to String.

3. What about going all the way from Query back to String?  (My naive
answer to my own question here is that some QueryNodeProcessor may
perform an irreversible operation, making it impossible to do this,
but I thought I would throw the question in anyway.)

Daniel


-- 
Daniel Noll                            Forensic and eDiscovery Software
Senior Developer                              The world's most advanced
Nuix                                                email data analysis
http://nuix.com/                                and eDiscovery software

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