Day-27 : Model 一对多

续上一篇，今天要来讲的是一对多
还记得吗？我们昨天说的
我们希望每一间商店可以贩售许多种商品，这就是我们所谓的一对多！

1. 建立 Product Model
   

2.执行 rails db:migrate

3. Store Model 加上has_many将设定成为（一对多）
   

4.反之，在Product Model 加上belongs_to

以上，这些动作，他大概的关联图如下表：

老样子，我们进 rails c 看看

1. 找出一间商店

 > store1 = Store.first
   (0.5ms)  SELECT sqlite_version(*)
  Store Load (0.1ms)  SELECT "stores".* FROM "stores" ORDER BY "stores"."id" ASC LIMIT ?  [["LIMIT", 1]]
 => #<Store id: 1, title: "良心商店", tel: nil, address: nil, user_id: 1, created_at: "2021-10-10 09:...

2.建立两件商品的资料，分别是product1和product2

> product1 = Product.new(name:"吃吃喝喝商店",price: 200)
 => #<Product id: nil, name: "吃吃喝喝商店", description: nil, price: 0.2e3, is_available: nil, store...
 > product2 = Product.new(name:"我想要飞",price: 1000)
 => #<Product id: nil, name: "我想要飞", description: nil, price: 0.1e4, is_available: nil, store_id:...

3.把这两个商品用阵列的方式，丢进去给store1

 > store1.products = [product1, product2]
  Product Load (0.4ms)  SELECT "products".* FROM "products" WHERE "products"."store_id" = ?  [["store_id", 1]]
  TRANSACTION (0.1ms)  begin transaction
  Product Create (0.4ms)  INSERT INTO "products" ("name", "price", "store_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?)  [["name", "吃吃喝喝商店"], ["price", 200.0], ["store_id", 1], ["created_at", "2021-10-11 08:29:21.580320"], ["updated_at", "2021-10-11 08:29:21.580320"]]
  Product Create (0.1ms)  INSERT INTO "products" ("name", "price", "store_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?)  [["name", "我想要飞"], ["price", 1000.0], ["store_id", 1], ["created_at", "2021-10-11 08:29:21.581872"], ["updated_at", "2021-10-11 08:29:21.581872"]]
  TRANSACTION (0.5ms)  commit transaction
 => [#<Product id: 1, name: "吃吃喝喝商店", description: nil, price: 0.2e3, is_available: nil, store_...

4.接下来，让我们来看看，资料是不是真的有写进去

> store1.products
 => #<ActiveRecord::Associations::CollectionProxy [
 #<Product id: 1, name: "吃吃喝喝商店", description: nil, price: 0.2e3, is_available: nil, store_id: 1, created_at: "2021-10-11 08:29:21.580320000 +0000", updated_at: "2021-10-11 08:29:21.580320000 +0000">, 
 #<Product id: 2, name: "我想要飞", description: nil, price: 0.1e4, is_available: nil, store_id: 1, created_at: "2021-10-11 08:29:21.581872000 +0000", updated_at: "2021-10-11 08:29:21.581872000 +0000">
 ]>

5.确认这些资料有几笔？

> store1.products.count
   (0.5ms)  SELECT COUNT(*) FROM "products" WHERE "products"."store_id" = ?  [["store_id", 1]]
 => 2

今天就先到这边，明天我们来讲多对多！
最近刚好有在练习这区块，就把一些书上的重点来写一篇。
看看自己在步骤上面是否有记住
希望飞得慢，可以成功抵达终点拉～

参考资料：为自己学Ruby on Rails