sortablegridfield/docs/HasManyExample.md

:::php
/*** TestPage.php ***/
class TestPage extends Page {
	public static $has_many=array(
		'TestObjects'=>'TestObject'
	);
	
	public function getCMSFields() {
		$fields=parent::getCMSFields();
		
		$conf=GridFieldConfig_RelationEditor::create(10);
		$conf->addComponent(new GridFieldSortableRows('SortOrder'));
		
		$fields->addFieldToTab('Root.TestObjects', new GridField('TestObjects', 'TestObjects', $this->TestObjects(), $conf));
		
		return $fields;
	}
}


/*** TestObject.php ***/
class TestObject extends DataObject {
	public static $db=array(
		'Title'=>'Text'
	);
	
	public static $belongs_many_many=array(
		'TestPages'=>'TestPage'
	);
	
	public static $default_sort='SortOrder';
}