Rails一對多關聯查詢

Question

楷模：

class User < ActiveRecord::Base
  has_may :friends
end

class Friend < ActiveRecord::Base
  belongs_to :user
end

表格：

要查詢：

都具有的users ：

friends.name = "Lily" 
# and 
friends.name = "Steven"

我想要按Model Where Query這樣：

User.joins(xxx).where(xxx)

有什么辦法嗎？

Answer 1

我認為

User.joins(:friends).where("friends.name = 'Lily' OR friends.name = 'Steven'")

會做你想要的

Answer 2

SELECT users.id, users.name 
FROM users 
INNER JOIN friends ON users.id = friends.user_id 
WHERE friends.name IN ('Lily', 'Steven') 
GROUP BY users.id 
HAVING COUNT(*) = 2;

ActiveRecord查詢

names = ['Lily', 'Steven']

User.select('users.id, users.name').joins(:friends).where(friends: { name: names }).group('users.id').having("COUNT(*) = #{names.count}")

SQLFiddle

上面的查詢將僅向您返回與"Lily"和"Steven"成為好友的用戶