hainan/app/Admin/Controllers/CategoryController.php

<?php

namespace App\Admin\Controllers;

use App\Models\Category;
use App\Models\Product;
use Dcat\Admin\Admin;
use Dcat\Admin\Form;
use Dcat\Admin\Grid;
use Dcat\Admin\Layout\Content;
use Dcat\Admin\Layout\Row;
use Dcat\Admin\Show;
use Dcat\Admin\Http\Controllers\AdminController;
use Dcat\Admin\Tree;

class CategoryController extends AdminController
{
	public function index(Content $content)
	{
		return $content->header('产品分类')
			->body(function (Row $row) {
				$tree = new Tree(new Category);
				$tree->expand();
				$tree->query(function ($model) {
					//agent_id为0是系统分类，其它是代理商分类
					return $model->where('agent_id', 0);
				});
				$row->column(12, $tree);
			});
	}

    /**
     * Make a grid builder.
     *
     * @return Grid
     */
    protected function grid()
    {
        return Grid::make(new Category(), function (Grid $grid) {
            $grid->column('id')->sortable();
            $grid->column('pid');
            $grid->column('name');
            $grid->column('sort');
        });
    }

    /**
     * Make a show builder.
     *
     * @param mixed $id
     *
     * @return Show
     */
    protected function detail($id)
    {
        return Show::make($id, new Category(), function (Show $show) {
            $show->field('id');
            $show->field('pid');
            $show->field('name');
            $show->field('sort');
        });
    }

    /**
     * Make a form builder.
     *
     * @return Form
     */
    protected function form()
    {
        return Form::make(new Category(), function (Form $form) {
			$options = Category::selectOptions(fn($query) => $query->where('agent_id', 0));

            $form->display('id');
            $form->select('pid')->options($options)->required();
            $form->text('name')->required();
            $form->text('sort')->default(255)->help('越小越靠前');
        })->saving(function (Form $form) {
			//不允许编辑的字段
			$form->ignore(['id', 'deleted_at']);

        	//后台管理员的agent_id为0
			$form->agent_id = 0;
			$form->sort = $form->sort ?? 255;
        })->deleting(function (Form $form) {
			//获取到要删除分类的ID
			$category_id = (int)$form->getKey();

			//获取要删除类目的所有下级ID
			$category = Category::where('agent_id', 0)->pluck('pid', 'id')->toArray();
			$ids = getChildCate($category_id, $category);

			if (Product::query()->whereIn('category_id', $ids)->exists()) {
				return $form->response()->error('该分类下已经发布产品，不允许删除');
			}
			return $form->response()->error('不允许删除');
		});
    }
}

//获取$pid下的所有子类目
function getChildCate($pid, $category): array
{
	$cate_arr = [$pid];
	foreach ($category as $k => $v) {
		if ($v == $pid) {
			$cate_arr = array_merge($cate_arr, getChildCate($k, $category));
		}
	}
	return $cate_arr;
}