ruby on rails - How to query for the products belonging to category and sub categories the correct way -

categories , sub categories independent models. , each category have sub categories.

while creating product, admin has select category , sub category.

following models have come with

class product < activerecord::base     belongs_to :category end  class category < activerecord::base   has_many :products end  class sub < activerecord::base    has_many :products end 

here schema products

create_table "products", force: :cascade |t|     t.string   "name"     t.integer  "price"     t.integer  "category_id"     t.integer  "sub_id"   end 

the product created this

product.create(name: "messi magnet custom",category_id: 1, sub_id: 2) 

and querying products belong particular category , sub category this

product.where("category_id = ? , sub_id = ?",9,3) 

is there thing wrong associations having? , improve this?

class category < activerecord::base   has_many :products   has_many :sub_categories end  class subcategory < activerecord::base   has_many :products   belongs_to :category   #sub_categories table have reference category, i.e., category_id column end  class product < activerecord::base   belongs_to :category   belongs_to :sub #you need add end