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<div class="document" id="value-ranges">
<h1 class="title">Value Ranges</h1>
<div class="contents topic" id="table-of-contents">
<p class="topic-title first">Table of contents</p>
<ul class="simple">
<li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li>
<li><a class="reference internal" href="#stringvaluerangeprocessor" id="id2">StringValueRangeProcessor</a></li>
<li><a class="reference internal" href="#datevaluerangeprocessor" id="id3">DateValueRangeProcessor</a></li>
<li><a class="reference internal" href="#numbervaluerangeprocessor" id="id4">NumberValueRangeProcessor</a></li>
<li><a class="reference internal" href="#custom-subclasses" id="id5">Custom subclasses</a></li>
<li><a class="reference internal" href="#using-several-valuerangeprocessors" id="id6">Using Several ValueRangeProcessors</a></li>
</ul>
</div>
<div class="section" id="introduction">
<h1><a class="toc-backref" href="#id1">Introduction</a></h1>
<p>The <tt class="docutils literal"><span class="pre">Xapian::ValueRangeProcessor</span></tt> was introduced in Xapian 1.0.0. It
provides a powerful and flexible way to parse range queries in the users'
query string.</p>
<p>This document describes the <tt class="docutils literal"><span class="pre">Xapian::ValueRangeProcessor</span></tt> class and
its standard subclasses, how to create your own subclasses, and how
these classes are used with <tt class="docutils literal"><span class="pre">Xapian::QueryParser</span></tt>.</p>
<p><tt class="docutils literal"><span class="pre">Xapian::ValueRangeProcessor</span></tt> is a virtual base class, so you need to
use a subclass of it. <tt class="docutils literal"><span class="pre">Xapian::QueryParser</span></tt> maintains a list of
<tt class="docutils literal"><span class="pre">Xapian::ValueRangeProcessor</span></tt> objects which it tries in order for
each range search in the query until one accepts it, or all have been
tried (in which case an error is reported).</p>
<p>Each <tt class="docutils literal"><span class="pre">Xapian::ValueRangeProcessor</span></tt> is passed the start and end of the
range. If it doesn't understand the range, it should return
<tt class="docutils literal"><span class="pre">Xapian::BAD_VALUENO</span></tt>. If it does understand the range, it should return
the value number to use with <tt class="docutils literal"><span class="pre">Xapian::Query::OP_VALUE_RANGE</span></tt> and if it
wants to, it can modify the start and end values (to convert them to the
correct format so that for the string comparison which <tt class="docutils literal"><span class="pre">OP_VALUE_RANGE</span></tt>
uses).</p>
<p>In Xapian 1.2.1 and later, <tt class="docutils literal"><span class="pre">Xapian::QueryParser</span></tt> supports open-ended
ranges - if the start of the range is empty, that means any value less than
the end, and similarly if the end is empty, that means any value greater
than the start. The start and end can't both be empty.</p>
</div>
<div class="section" id="stringvaluerangeprocessor">
<h1><a class="toc-backref" href="#id2">StringValueRangeProcessor</a></h1>
<p>This is the simplest of the standard subclasses. It understands any range
passed (so it should always be the last <tt class="docutils literal"><span class="pre">ValueRangeProcessor</span></tt>) and it
doesn't alter the range start or end.</p>
<p>For example, suppose you have stored author names in value number 4, and want
the user to be able to filter queries by specifying ranges of values such as:</p>
<pre class="literal-block">
mars asimov..bradbury
</pre>
<p>To do this, you can use a <tt class="docutils literal"><span class="pre">StringValueRangeProcessor</span></tt> like so:</p>
<pre class="literal-block">
Xapian::QueryParser qp;
Xapian::StringValueRangeProcessor author_proc(4);
qp.add_valuerangeprocessor(&author_proc);
</pre>
<p>The parsed query will use <tt class="docutils literal"><span class="pre">OP_VALUE_RANGE</span></tt>, so <tt class="docutils literal"><span class="pre">query.get_description()</span></tt>
would report:</p>
<pre class="literal-block">
Xapian::Query(mars:(pos=1) FILTER (VALUE_RANGE 4 asimov bradbury)
</pre>
<p>The <tt class="docutils literal"><span class="pre">VALUE_RANGE</span></tt> subquery will only match documents where value 4 is
>= asimov and <= bradbury (using a string comparison).</p>
</div>
<div class="section" id="datevaluerangeprocessor">
<h1><a class="toc-backref" href="#id3">DateValueRangeProcessor</a></h1>
<p>This class allows you to implement date range searches. As well as the value
number to search, you can tell it whether to prefer US-style month/day/year
or European-style day/month/year, and specify the epoch year to use for
interpreting 2 digit years (the default is day/month/year with an epoch of
1970). The best choice of settings depends on the expectations of your users.
As these settings are only applied at search time, you can also easily offer
different versions of your search front-end with different settings if that is
useful.</p>
<p>For example, if your users are American and the dates present in your database
can extend a decade or so into the future, you might use something like this
which specifies to prefer US-style dates and that the epoch year is 1930 (so
02/01/29 is February 1st 2029 while 02/01/30 is February 1st 1930):</p>
<pre class="literal-block">
Xapian::QueryParser qp;
Xapian::DateValueRangeProcessor date_proc(0, true, 1930);
qp.add_valuerangeprocessor(&date_proc);
</pre>
<p>The dates are converted to the format YYYYMMDD, so the values you index also
need to also be in this format - for example, if <tt class="docutils literal"><span class="pre">doc_time</span></tt> is a <tt class="docutils literal"><span class="pre">time_t</span></tt>:</p>
<pre class="literal-block">
char buf[9];
if (strftime(buf, sizeof(buf), "%Y%m%d", gmtime(&doc_time))) {
doc.add_value(0, buf);
}
</pre>
</div>
<div class="section" id="numbervaluerangeprocessor">
<h1><a class="toc-backref" href="#id4">NumberValueRangeProcessor</a></h1>
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">This class had a design flaw in Xapian 1.0.0 and 1.0.1 - you should
avoid using it with releases of Xapian earlier than 1.0.2.</p>
</div>
<p>This class allows you to implement numeric range searches. The numbers used
may be any number which is representable as a double, but requires that the
stored values which the range is being applied have been converted to strings
at index time using the <tt class="docutils literal"><span class="pre">Xapian::sortable_serialise()</span></tt> method:</p>
<pre class="literal-block">
Xapian::Document doc;
doc.add_value(0, Xapian::sortable_serialise(price));
</pre>
<p>This method produces strings which will sort in numeric order, so you can use
it if you want to be able to sort based on the value in numeric order, too.</p>
<p>The class allows a prefix or suffix to be specified which must be present on
the values, allowing multiple NumberValueRangeProcessors to be active in the
same queryparser. For example, this specifies that a prefix of "$" must be
present on the first value (and may optionally be present on the second
value):</p>
<pre class="literal-block">
Xapian::QueryParser qp;
Xapian::NumberValueRangeProcessor numrange_proc(0, "$", true);
qp.add_valuerangeprocessor(&numrange_proc);
</pre>
</div>
<div class="section" id="custom-subclasses">
<h1><a class="toc-backref" href="#id5">Custom subclasses</a></h1>
<p>You can easily create your own subclasses of <tt class="docutils literal"><span class="pre">Xapian::ValueRangeProcessor</span></tt>.
Your subclass needs to implement a method
<tt class="docutils literal"><span class="pre">Xapian::valueno</span> <span class="pre">operator()(std::string</span> <span class="pre">&begin,</span> <span class="pre">std::string</span> <span class="pre">&end)</span></tt>
so for example you could implement a better version of the author range
described above which only matches ranges with a prefix (e.g.
<tt class="docutils literal"><span class="pre">author:asimov..bradbury</span></tt>) and lower-cases the names:</p>
<pre class="literal-block">
struct AuthorValueRangeProcessor : public Xapian::ValueRangeProcessor {
AuthorValueRangeProcessor() {}
Xapian::valueno operator()(std::string &begin, std::string &end) {
if (begin.substr(0, 7) != "author:")
return Xapian::BAD_VALUENO;
begin.erase(0, 7);
begin = Xapian::Unicode::tolower(begin);
end = Xapian::Unicode::tolower(end);
return 4;
}
};
</pre>
<p>If you want to support open-ended ranges, you need to handle begin or end
being empty suitably. <tt class="docutils literal"><span class="pre">Xapian::QueryParser</span></tt> won't call your subclass
with both begin and end being empty.</p>
</div>
<div class="section" id="using-several-valuerangeprocessors">
<h1><a class="toc-backref" href="#id6">Using Several ValueRangeProcessors</a></h1>
<p>If you want to allow the user to specify different types of ranges, you can
specify multiple <tt class="docutils literal"><span class="pre">ValueRangeProcessor</span></tt> objects to use. Just add them in
the order you want them to be checked:</p>
<pre class="literal-block">
Xapian::QueryParser qp;
AuthorValueRangeProcessor author_proc();
qp.add_valuerangeprocessor(&author_proc);
Xapian::DateValueRangeProcessor date_proc(0, false, 1930);
qp.add_valuerangeprocessor(&date_proc);
</pre>
<p>And then you can parse queries such as
<tt class="docutils literal"><span class="pre">mars</span> <span class="pre">author:Asimov..Bradbury</span> <span class="pre">01/01/1960..31/12/1969</span></tt> successfully.</p>
</div>
</div>
</body>
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