laravel 关系使用 MySQL 加入

Question

I have a relation in my Product Model and it's working fine

        self::where('products.id', '=', $id)
        ->select('products.category_id', 'main_categories.id as main_category_id')
            ->join('categories', 'products.category_id', '=', 'categories.id')
                ->join('main_categories', 'categories.main_category_id', '=', 'main_categories.id')
                    ->first();

i have replaced it with

        self::where('products.id', '=', $id)
        ->select('products.category_id', 'categories.id as parent_id')
            ->join('categories', 'products.category_id', '=', 'categories.id')
                ->join('categories', 'categories.parent_id', '=', 'categories.id')
                    ->first();

Now i get this error

Syntax error or access violation: 1066 Not unique table/alias: 'categories' (SQL: select products . category_id , categories . id as parent_id from products inner join categories on products . category_id = categories . id inner join categories on categories . parent_id = categories . id where products . id = 13 limit 1)

Answer 1

You are using same table two times for joining without using any alias names.

please refer the below code

self::where('products.id', '=', $id)
        ->select('products.category_id', 'cate1.id as parent_id')
            ->join('categories as cate1', 'products.category_id', '=', 'cate1.id')
                ->join('categories as cate2', 'cate1.parent_id', '=', 'cate2.id')
                    ->first();

NOTE: hope, the parent_id you refered from cate1 . if not please, feel free to change the alias name to appropriate.