silverstripe-blog/src/Admin/GridFieldCategorisationConfig.php

<?php

namespace SilverStripe\Blog\Admin;

use SilverStripe\Blog\Forms\GridField\GridFieldAddByDBField;
use SilverStripe\Blog\Admin\GridFieldMergeAction;
use SilverStripe\Blog\Model\CategorisationObject;
use SilverStripe\Forms\GridField\GridFieldConfig_RecordEditor;

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, $mergeRecords, $parentType, $parentMethod, $childMethod)
    {
        parent::__construct($itemsPerPage);

        $this->removeComponentsByType('SilverStripe\\Forms\\GridField\\GridFieldAddNewButton');

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

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

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

        $columns->setFieldFormatting(
            [
                'BlogPostsCount' => function ($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('SilverStripe\\Forms\\GridField\\GridFieldDataColumns');

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