如何创建具有多个复杂关联/连接的 Rails 模型？

Question

我正在尝试弄清楚如何创建具有可以产生与此 SQL 查询相同结果的关联的 ActiveRecord 模型：

SELECT login, first_name, last_name, email_address 
FROM accounts 
INNER JOIN people ON person.id = accounts.person_id
INNER JOIN email_address_people ON person.id = email_address_people.person_id 
INNER JOIN email_addresses ON email_address.id = email_address_people.email_address_id
INNER JOIN email_address_types ON email_address_types.id = email_address_people.email_address_type_id 
WHERE email_address_types.email_address_type = 'account';

表结构如下，并假设每个表都有一个id 每个正常的 ActiveRecord 约定：

帐户
id : 整数
person_id : 整数
登录：字符串

人
id : 整数
名字：字符串
姓氏：字符串

email_address_people
id : 整数
person_id : 整数
email_address_id : 整数
email_address_type_id : int

电子邮件地址
id : 整数
电子邮件地址：字符串

email_address_types
id : 整数
email_address_type：字符串

我需要模型功能齐全，不受 :find_by_sql 之类的限制。

如何创建使这成为可能的关联模型？

谢谢！
克里斯·本森
chris@chrisbenson.com

Answer 1

试试这个：

你的模型类：

  class EmailAddress < ActiveRecord::Base
  end

  class EmailAddressType < ActiveRecord::Base
  end

  class People < ActiveRecord::Base
    has_many :accounts
    has_many :email_address_people
    has_many :email_addresses, :through => :email_address_people

    has_many :account_email_address_people, 
                   :class_name => "EmailAddressPeople", 
                   :conditions => "email_address_type = 'account'"

    has_many :account_email_addresses, 
                   :through => :account_email_address_people

  end

  class EmailAddressPeople < ActiveRecord::Base
    belongs_to :person
    belongs_to :email_address
    belongs_to :email_address_type
  end

您的帐户模型：

  class Account < ActiveRecord::Base
    belongs_to :person

    # now to the actual method
    def account_emails
      person.account_email_addresses.map do |email|
        [login, person.first_name, person.last_name, email.email_address]
      end
    end

    # Brute force SQL if you prefer
    def account_emails2
       sql = "YOUR SQL HERE"
       self.connection.select_values(sql)
    end

  end

假设您手头有 Account 对象 account.account_emails 进行两次数据库调用：

• 使用 id 获取人员

• 获取此人的帐户电子邮件

直接进入数据库（即account.account_emails2）是最快的选择，但不是 Rails 方式。

Answer 2

我认为最好的办法是先给你文档：http://railsbrain.com/api/rails-2.3.2/doc/index.html
查找“has_many”（注意 :through）和“belongs_to”，以及“has_one”，虽然我认为您不会使用后者。
This blog post 将帮助您处理 has_many ：通过概念 - 我认为在那之后，你会被设置。让我们知道是否有任何不清楚的地方！

class Account < ActiveRecord::Base
  belongs_to :person
end

class Person < ActiveRecord::Base
  has_many :accounts
  has_many :email_addresses :through => :email_address_people
end

class EmailAddress < ActiveRecord::Base
  belongs_to :email_address_type
  belongs_to :person
  has_one :email_address_type
end

class EmailAddressType < ActiveRecord::Base
  has_many :email_addresses :through => :email_address_people
end

我会开始的。它没有经过测试，但如果我们看到有什么问题，那么我们可以修复它.. :)