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<h1><span class="section-number">7.13. </span>grn_expr<a class="headerlink" href="#grn-expr" title="Permalink to this headline">¶</a></h1>
<p>Grn_expr is an object that searches records with specified conditions
and manipulates a database. It’s pronounced as <code class="docutils literal notranslate"><span class="pre">gurun</span> <span class="pre">expression</span></code>.</p>
<p>Conditions for searching records from a database can be represented by
conbining condition expressions such as <code class="docutils literal notranslate"><span class="pre">equal</span> <span class="pre">condition</span> <span class="pre">expression</span></code>
and <code class="docutils literal notranslate"><span class="pre">less</span> <span class="pre">than</span> <span class="pre">condition</span> <span class="pre">expression</span></code> with set operations such as
<code class="docutils literal notranslate"><span class="pre">AND</span></code>, <code class="docutils literal notranslate"><span class="pre">OR</span></code> and <code class="docutils literal notranslate"><span class="pre">NOT</span></code>. Grn_expr executes those conditions to
search records. You can also use advanced searches such as similar
search and near search by grn_expr. You can also use flexible full
text search. For example, you can control hit scores for specified
words and improve recall by re-searching with high-recall algolithm
dinamically. To determine whether re-searching or not, the number of
matched rescords is used.</p>
<p>There are three ways to create grn_expr:</p>
<blockquote>
<div><ul class="simple">
<li><p>Parsing <a class="reference internal" href="grn_expr/query_syntax.html"><span class="doc">Query syntax</span></a> string.</p></li>
<li><p>Parsing <a class="reference internal" href="grn_expr/script_syntax.html"><span class="doc">Script syntax</span></a> string.</p></li>
<li><p>Calling grn_expr related APIs.</p></li>
</ul>
</div></blockquote>
<p><a class="reference internal" href="grn_expr/query_syntax.html"><span class="doc">Query syntax</span></a> is for common search form in
Internet search site. It’s simple and easy to use but it has a
limitation. You can not use all condition expressions and set
operations in <a class="reference internal" href="grn_expr/query_syntax.html"><span class="doc">Query syntax</span></a>. You can use
<a class="reference internal" href="grn_expr/query_syntax.html"><span class="doc">Query syntax</span></a> with <code class="docutils literal notranslate"><span class="pre">query</span></code> option in
<a class="reference internal" href="commands/select.html"><span class="doc">select</span></a>.</p>
<p><a class="reference internal" href="grn_expr/script_syntax.html"><span class="doc">Script syntax</span></a> is ECMAScript like
syntax. You can use all condition expressions and set operations in
<a class="reference internal" href="grn_expr/script_syntax.html"><span class="doc">Script syntax</span></a>. You can use
<a class="reference internal" href="grn_expr/script_syntax.html"><span class="doc">Script syntax</span></a> with <code class="docutils literal notranslate"><span class="pre">filter</span></code> option and
<code class="docutils literal notranslate"><span class="pre">scorer</span></code> option in <a class="reference internal" href="commands/select.html"><span class="doc">select</span></a>.</p>
<p>You can use groonga as a library and create a grn_expr by calling
grn_expr related APIs. You can use full features with calling APIs
like <a class="reference internal" href="grn_expr/script_syntax.html"><span class="doc">Script syntax</span></a>. Calling APIs is useful
creating a custom syntax to create grn_expr. They are used in <a class="reference external" href="http://ranguba.org/#about-rroonga">rroonga</a> that is Ruby bindings
of Groonga. Rroonga can create a grn_expr by Ruby’s syntax instead of
parsing string.</p>
<div class="toctree-wrapper compound">
<ul>
<li class="toctree-l1"><a class="reference internal" href="grn_expr/query_syntax.html">7.13.1. Query syntax</a></li>
<li class="toctree-l1"><a class="reference internal" href="grn_expr/script_syntax.html">7.13.2. Script syntax</a></li>
</ul>
</div>
<div class="section" id="see-also">
<h2><span class="section-number">7.13.3. </span>See also<a class="headerlink" href="#see-also" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div><ul class="simple">
<li><p><a class="reference internal" href="api/grn_expr.html"><span class="doc">grn_expr</span></a>: grn_expr related APIs</p></li>
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