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<div class="sub-title"><span class="package-label-in-type">Package</span>&nbsp;<a href="package-summary.html">org.apache.calcite.schema</a></div>
<h1 title="Interface FunctionContext" class="title">Interface FunctionContext</h1>
</div>
<section class="class-description" id="class-description">
<hr>
<div class="type-signature"><span class="modifiers">public interface </span><span class="element-name type-name-label">FunctionContext</span></div>
<div class="block">Information about a function call that is passed to the constructor of a
function instance.
<p>This may enable a function to perform work up front, during construction,
rather than each time it is invoked. Here is an example of such a function:
<blockquote><pre>
class RegexMatchesFunction {
final java.util.regex.Pattern pattern;
public RegexMatchesFunction(FunctionContext cx) {
String pattern = cx.argumentValueAs(String.class);
this.compiledPattern = java.util.regex.Pattern.compile(pattern);
}
public boolean eval(String pattern, String s) {
return this.compiledPattern.matches(s);
}
}
</pre></blockquote>
<p>Register it in the model as follows:
<blockquote><pre>
functions: [
{
name: 'REGEX_MATCHES',
className: 'com.example.RegexMatchesFun'
}
]
</pre></blockquote>
<p>and use it in a query:
<blockquote><pre>
SELECT empno, ename
FROM Emp
WHERE regex_matches('J.*ES', ename);
+-------+--------+
| EMPNO | ENAME |
+-------+--------+
| 7900 | JAMES |
| 7566 | JONES |
+-------+--------+
</pre></blockquote>
<p>When executing the query, Calcite will create an instance of
<code>RegexMatchesFunction</code> and call the <code>eval</code> method on that
instance once per row.
<p>If the <code>eval</code> method was static, or if the function's
constructor had zero parameters, the <code>eval</code> method would have to call
<code>java.util.regex.Pattern.compile(pattern)</code> to compile the pattern each
time.
<p>This interface is marked <a href="../linq4j/function/Experimental.html" title="annotation in org.apache.calcite.linq4j.function"><code>Experimental</code></a>, which means that we may
change or remove methods, or the entire interface, without notice. But
probably we will add methods over time, which will just your UDFs more
information to work with.</div>
</section>
<section class="summary">
<ul class="summary-list">
<!-- ========== METHOD SUMMARY =========== -->
<li>
<section class="method-summary" id="method-summary">
<h2>Method Summary</h2>
<div id="method-summary-table">
<div class="table-tabs" role="tablist" aria-orientation="horizontal"><button id="method-summary-table-tab0" role="tab" aria-selected="true" aria-controls="method-summary-table.tabpanel" tabindex="0" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table', 3)" class="active-table-tab">All Methods</button><button id="method-summary-table-tab2" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab2', 3)" class="table-tab">Instance Methods</button><button id="method-summary-table-tab3" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab3', 3)" class="table-tab">Abstract Methods</button></div>
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<div class="summary-table three-column-summary" aria-labelledby="method-summary-table-tab0">
<div class="table-header col-first">Modifier and Type</div>
<div class="table-header col-second">Method</div>
<div class="table-header col-last">Description</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code>&lt;V&gt;&nbsp;@Nullable V</code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#getArgumentValueAs(int,java.lang.Class)" class="member-name-link">getArgumentValueAs</a><wbr>(int&nbsp;ordinal,
<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Class.html" title="class or interface in java.lang" class="external-link">Class</a>&lt;V&gt;&nbsp;valueClass)</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Returns the value of an argument to this function,
null if the argument is the NULL literal.</div>
</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code>int</code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#getParameterCount()" class="member-name-link">getParameterCount</a>()</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Returns the number of parameters.</div>
</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="../rel/type/RelDataTypeFactory.html" title="interface in org.apache.calcite.rel.type">RelDataTypeFactory</a></code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#getTypeFactory()" class="member-name-link">getTypeFactory</a>()</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Returns the type factory.</div>
</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code>boolean</code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#isArgumentConstant(int)" class="member-name-link">isArgumentConstant</a><wbr>(int&nbsp;ordinal)</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3">
<div class="block">Returns whether the value of an argument is constant.</div>
</div>
</div>
</div>
</div>
</section>
</li>
</ul>
</section>
<section class="details">
<ul class="details-list">
<!-- ============ METHOD DETAIL ========== -->
<li>
<section class="method-details" id="method-detail">
<h2>Method Details</h2>
<ul class="member-list">
<li>
<section class="detail" id="getTypeFactory()">
<h3>getTypeFactory</h3>
<div class="member-signature"><span class="return-type"><a href="../rel/type/RelDataTypeFactory.html" title="interface in org.apache.calcite.rel.type">RelDataTypeFactory</a></span>&nbsp;<span class="element-name">getTypeFactory</span>()</div>
<div class="block">Returns the type factory.</div>
</section>
</li>
<li>
<section class="detail" id="getParameterCount()">
<h3>getParameterCount</h3>
<div class="member-signature"><span class="return-type">int</span>&nbsp;<span class="element-name">getParameterCount</span>()</div>
<div class="block">Returns the number of parameters.</div>
</section>
</li>
<li>
<section class="detail" id="isArgumentConstant(int)">
<h3>isArgumentConstant</h3>
<div class="member-signature"><span class="return-type">boolean</span>&nbsp;<span class="element-name">isArgumentConstant</span><wbr><span class="parameters">(int&nbsp;ordinal)</span></div>
<div class="block">Returns whether the value of an argument is constant.</div>
<dl class="notes">
<dt>Parameters:</dt>
<dd><code>ordinal</code> - Argument ordinal, starting from 0</dd>
</dl>
</section>
</li>
<li>
<section class="detail" id="getArgumentValueAs(int,java.lang.Class)">
<h3>getArgumentValueAs</h3>
<div class="member-signature"><span class="type-parameters">&lt;V&gt;</span>&nbsp;<span class="return-type">@Nullable V</span>&nbsp;<span class="element-name">getArgumentValueAs</span><wbr><span class="parameters">(int&nbsp;ordinal,
<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Class.html" title="class or interface in java.lang" class="external-link">Class</a>&lt;V&gt;&nbsp;valueClass)</span></div>
<div class="block">Returns the value of an argument to this function,
null if the argument is the NULL literal.</div>
<dl class="notes">
<dt>Parameters:</dt>
<dd><code>ordinal</code> - Argument ordinal, starting from 0</dd>
<dd><code>valueClass</code> - Type of value</dd>
<dt>Throws:</dt>
<dd><code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/ClassCastException.html" title="class or interface in java.lang" class="external-link">ClassCastException</a></code> - if argument cannot be converted to
<code>valueClass</code></dd>
<dd><code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/IllegalArgumentException.html" title="class or interface in java.lang" class="external-link">IllegalArgumentException</a></code> - if argument is not constant</dd>
</dl>
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