php-doc-en/reference/mongo/mongocursor/explain.xml

<?xml version="1.0" encoding="utf-8"?>

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<refentry xml:id="mongocursor.explain" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>MongoCursor::explain</refname>
  <refpurpose>Return an explanation of the query, often useful for optimization and debugging</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <modifier>public</modifier> <type>array</type><methodname>MongoCursor::explain</methodname>
   <void/>
  </methodsynopsis>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  &no.function.parameters;
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;  
  <para>
   Returns an explanation of the query.
  </para>
 </refsect1>
 <refsect1 role="examples">
  &reftitle.examples;
  <example>
   <title><function>MongoCursor::explain</function> example</title>
   <programlisting role="php">
<![CDATA[
<?php

$cursor = $collection->find(array("x"=>1), array("y"));
$cursor->sort(array("z" => 1))->limit(4)->skip(5);

var_dump($cursor->explain());

?>
]]>
   </programlisting>
   &example.outputs.similar;
   <screen>
<![CDATA[
array(8) {
  ["cursor"]=>
  string(15) "BtreeCursor x_1"
  ["startKey"]=>
  array(1) {
    ["x"]=>
    int(1)
  }
  ["endKey"]=>
  array(1) {
    ["x"]=>
    int(1)
  }
  ["nscanned"]=>
  float(4)
  ["n"]=>
  int(4)
  ["scanAndOrder"]=>
  int(1)
  ["millis"]=>
  int(3)
  ["allPlans"]=>
  array(2) {
    [0]=>
    array(3) {
      ["cursor"]=>
      string(15) "BtreeCursor x_1"
      ["startKey"]=>
      array(1) {
        ["x"]=>
        int(1)
      }
      ["endKey"]=>
      array(1) {
        ["x"]=>
        int(1)
      }
    }
    [1]=>
    array(3) {
      ["cursor"]=>
      string(11) "BasicCursor"
      ["startKey"]=>
      array(0) {
      }
      ["endKey"]=>
      array(0) {
      }
    }
  }
}
]]>
   </screen>
  </example>
 </refsect1>
 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   Throws <classname>MongoConnectionException</classname> if it cannot reach the 
   database.
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   MongoDB core docs on <link xlink:href="&url.mongodb.dochub.explain;">explain</link>.
  </para>
 </refsect1>

</refentry>
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