Adding multiple maps to a page using Mappable for SilverStripe 3

_config.php

Object::add_extension('ContactPageAddress','MapExtension');

ContactPage.php

<?php
class ContactPage extends DemoPage {

  static $has_many = array(
    'Locations' => 'ContactPageAddress'
  );

  function getCMSFields() {
    $fields = parent::getCMSFields();

    $gridConfig = GridFieldConfig_RelationEditor::create();
    $gridConfig->getComponentByType( 'GridFieldAddExistingAutocompleter' )->setSearchFields( array( 'PostalAddress' ) );
    $gridConfig->getComponentByType( 'GridFieldPaginator' )->setItemsPerPage( 100 );
    $gridField = new GridField( "Locations", "List of Addresses:", $this->Locations(), $gridConfig );
    $fields->addFieldToTab( "Root.Addresses", $gridField );

    return $fields;
  }
}

class ContactPage_Controller extends Page_Controller {


}

?>

ContactPage.ss

<% require css(weboftalent-mappable-demo/css/mapdemo.css) %>

<h1>$Title</h1>
$BriefDescription

<h2>Addresses</h2>

<% loop Locations %>
<h3>$PostalAddress</h3>
$BasicMap
<% end_loop %>

$Content

ContactPageAddress.php

<?php
class ContactPageAddress extends DataObject {
	static $db = array(
		'PostalAddress' => 'Text'
	);

	static $has_one = array( 'ContactPage' => 'ContactPage' );


	public static $summary_fields = array(
		'PostalAddress' => 'PostalAddress'
	);


	function getCMSFields() {
		$fields = new FieldList();
		$fields->push( new TabSet( "Root", $mainTab = new Tab( "Main" ) ) );
		$mainTab->setTitle( _t( 'SiteTree.TABMAIN', "Main" ) );
		$fields->addFieldToTab( "Root.Main", new TextField( 'PostalAddress' ) );

		$this->extend( 'updateCMSFields', $fields );

		return $fields;
	}
}
?>