1:N 一對多

如果我們希望每間商店可以販售許多種飲料，可以使用一對多模式來進行關連。

先建立 Drink 這個 Model：
rails g model Drink name price:decimal store_id:integer

目前的資料關聯設計像下圖

先把 model 之間的關聯建立好

drink.rb

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class Drink < ApplicationRecord
  belongs_to :stores
end

store.rb

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class Store < ApplicationRecord
  has_many :drinks
  belongs_to :owner
end

方法建立

跟 has_one 一樣，設定 has_many :drinks 後會多了以下幾個方法，belongs_to 建立的方法跟 1:1 是一樣，這邊就不多提：

drinks
drinks=
build
create

console 測試看看

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# 找回上次建立的飲料店
s1 = Store.last

id: 1,
name: "五石蘭",
tel: "031234567",
address: "新竹縣",
owner_id: 1,
created_at: Fri, 07 Oct 2022 07:22:23.353390000 UTC +00:00,
updated_at: Fri, 07 Oct 2022 07:22:23.353390000 UTC +00:00>

# 直接用 Drink 建立好再丟給 store
d1 = Drink.new(name:"紅茶", price:30)

id: 1,
name: "紅茶",
price: 0.6e2,
store_id: 1,
created_at: Fri, 07 Oct 2022 07:52:50.417919000 UTC +00:00,
updated_at: Fri, 07 Oct 2022 07:52:50.417919000 UTC +00:00>,

#1 把 d1 放到陣列中指定給 s1.drinks
s1.drinks = [d1]

#2 把 d1 插入到 s1.drinks 陣列
s1.drinks << d1

# 透過 store 去建立 drink
s1.drinks.create(name:"珍珠奶茶", price:60)

id: 2,
name: "珍珠奶茶",
price: 0.6e2,
store_id: 1,
created_at: Fri, 07 Oct 2022 07:54:55.118310000 UTC +00:00,
updated_at: Fri, 07 Oct 2022 07:54:55.118310000 UTC +00:00>]

查出所有 s1 的飲料

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s1.drinks

id: 1,
name: "紅茶",
price: 0.3e2,
store_id: 1,
created_at: Fri, 07 Oct 2022 07:52:50.417919000 UTC +00:00,
updated_at: Fri, 07 Oct 2022 07:52:50.417919000 UTC +00:00>,
id: 2,
name: "珍珠奶茶",
price: 0.6e2,
store_id: 1,
created_at: Fri, 07 Oct 2022 07:54:55.118310000 UTC +00:00,
updated_at: Fri, 07 Oct 2022 07:54:55.118310000 UTC +00:00>]

也可以反查出某款飲料是哪間店

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# 找回最後建立的飲料(珍珠奶茶)
d2 = Drink.last

id: 2,
name: "珍珠奶茶",
price: 0.6e2,
store_id: 1,
created_at: Fri, 07 Oct 2022 07:54:55.118310000 UTC +00:00,
updated_at: Fri, 07 Oct 2022 07:54:55.118310000 UTC +00:00>]

# 因為 belongs_to 可以利用 store 方法反查
d2.store
 id: 1,
 name: "五石蘭",
 tel: "031234567",
 address: "新竹縣",
 owner_id: 1,
 created_at: Fri, 07 Oct 2022 07:22:23.353390000 UTC +00:00,
 updated_at: Fri, 07 Oct 2022 07:22:23.353390000 UTC +00:00>

參考資料：

  1. 為你自己學 Ruby on Rails