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<refentry xml:id="mongocollection.ensureindex" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>MongoCollection::ensureIndex</refname>
  <refpurpose>
   Creates an index on the given field(s), or does nothing if the index 
   already exists
  </refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <modifier>public</modifier> <type>boolean</type><methodname>MongoCollection::ensureIndex</methodname>
   <methodparam><type>array</type><parameter>keys</parameter></methodparam>
   <methodparam><type>array</type><parameter>options</parameter></methodparam>
  </methodsynopsis>
  <para>
   A unique index cannot be created on a field if multiple existing documents do
   not contain the field.  The field is effectively &null; for these documents 
   and thus already non-unique.
  </para>
 </refsect1>

 <refsect1 role="parameters"> 
  &reftitle.parameters; 
  <para>
   <variablelist>
    <varlistentry>
     <term>
      <parameter>keys</parameter>
     </term>
     <listitem>
      <para>
       Field or fields to use as index.
      </para>
     </listitem>
    </varlistentry>   
    <varlistentry>
     <term>
      <parameter>options</parameter>
     </term>
     <listitem>
      <para>
       This parameter is an associative array of the form 
       <literal>array("optionname" => &lt;boolean&gt;, ...)</literal>. Currently 
       supported options are: 
       <itemizedlist>
        <listitem>
         <para>
          <literal>"unique"</literal>
         </para>
         <para>
          Create a unique index.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>"dropDups"</literal>
         </para>
         <para>
          If a unique index is being created and duplicate values exist, drop
          all but one duplicate value.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>"background"</literal>
         </para>
         <para>
          If you are using MongoDB version 1.3.2+, you can create indexes in the
          background while other operations are taking place.  By default, index
          creation happens synchronously.  If you specify &true; with this 
          option, index creation will be asynchronous.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>"safe"</literal>
         </para>
         <para>
          Starting with driver version 1.0.4, you can specify a boolean value 
          for checking if the index creation succeeded.  The driver will throw
          a MongoCursorException if index creation failed.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>"name"</literal>
         </para>
         <para>
          After driver version 1.0.4 (NOT including 1.0.4) you can specify an
          index name.  This can be useful if you are indexing many keys and 
          Mongo complains about the index name being too long.
         </para>
        </listitem>
       </itemizedlist>
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns &true;.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>1.0.2</entry>
       <entry>
        Changed "options" parameter from boolean to array.  Pre-1.0.2, the
        second parameter was an optional boolean value specifying a unique 
        index.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <example>
   <title><function>MongoCollection::ensureIndex</function> example</title>
   <programlisting role="php">
<![CDATA[
<?php

$c = new MongoCollection($db, 'foo');

// create an index on 'x' ascending
$c->ensureIndex(array('x' => 1));

// create an index on 'z' ascending and 'zz' descending
$c->ensureIndex(array('z' => 1, 'zz' => -1));

// create a unique index on 'x'
$c->ensureIndex(array('x' => 1), array("unique" => true));

?>
]]>
   </programlisting>
  </example>
  <example>
   <title>Drop duplicates example</title>
   <programlisting role="php">
<![CDATA[
<?php

$collection->insert(array("username" => "joeschmoe"));
$collection->insert(array("username" => "joeschmoe"));

/*
 * index creation fails, you can't create a unique index on a key with 
 * non-unique values
 */
$collection->ensureIndex(array("username" => 1), array("unique" => 1));

/*
 * index creation succeeds: one of the documents is removed from the collection
 */
$collection->ensureIndex(array("username" => 1), array("unique" => 1, "dropDups" => 1));

/* 
 * now we have a unique index, more inserts with the same username (such as the
 * one below) will fail
 */
$collection->insert(array("username" => "joeschmoe"));

?>
]]>
   </programlisting>
  </example>

  <example>
   <title>Geospatial Indexing</title>
   <para>
    Mongo supports geospatial indexes, which allow you to search for documents
    near a given location or within a shape.  For example, to create a 
    geospatial index on the "loc" field:
   </para>
   <programlisting role="php">
<![CDATA[
<?php

$collection->ensureIndex(array("loc" => "2d"));

?>
]]>
   </programlisting>
  </example>
 </refsect1>

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

</refentry>
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