silverstripe-blog/code/admin/GridFieldCategorisationConfig.php

<?php

class GridFieldCategorisationConfig extends GridFieldConfig_RecordEditor {
	/**
	 * @param int $itemsPerPage
	 * @param array|SS_List $mergeRecords
	 * @param string $parentType
	 * @param string $parentMethod
	 * @param string $childMethod
	 */
	public function __construct($itemsPerPage = 15, $mergeRecords, $parentType, $parentMethod, $childMethod) {
		parent::__construct($itemsPerPage);

		$this->removeComponentsByType('GridFieldAddNewButton');

		$this->addComponent(
			new GridFieldAddByDBField('buttons-before-left')
		);

		$this->addComponent(
			new GridFieldMergeAction($mergeRecords, $parentType, $parentMethod, $childMethod)
		);

		/**
		 * @var GridFieldDataColumns $columns
		 */
		$columns = $this->getComponentByType('GridFieldDataColumns');

		$columns->setFieldFormatting(array(
			'BlogPostsCount' => function ($value, CategorisationObject $item) {
				return $item->BlogPosts()->Count();
			}
		));

		$this->changeColumnOrder();
	}

	/**
	 * Reorders GridField columns so that Actions is last.
	 */
	protected function changeColumnOrder() {
		/**
		 * @var GridFieldDataColumns $columns
		 */
		$columns = $this->getComponentByType('GridFieldDataColumns');

		$columns->setDisplayFields(array(
			'Title' => 'Title',
			'BlogPostsCount' => 'Posts',
			'MergeAction' => 'MergeAction',
			'Actions' => 'Actions',
		));
	}
}