Ruby on Rails的连接表关联 [英] Ruby on Rails Join Table Associations

问题描述

我有一个Ruby on Rails应用程序设置像这样：

I have a Ruby on Rails application setup like so:

用户模型

has_and_belongs_to_many :roles

角色模型

has_many :transactions
has_and_belongs_to_many :users

事务模型

belongs_to :role

这意味着连接表是用于一个名为 roles_users ，这也意味着用户只能看到已经通过角色被分配给他们的交易，使用示例：

This means that a join table is used called roles_users and it also means that a user can only see the transactions that have been assigned to them through roles, usage example:

user = User.find(1)
transactions = user.roles.first.transactions

这将返回它们与分配给用户的第一角色相关联的事务。如果用户有分配给他们，此刻2角色获得与我会做第二角色相关联的交易：

This will return the transactions which are associated with the first role assigned to the user. If a user has 2 roles assigned to them, at the moment to get the transactions associated with the second role I would do:

transactions = user.roles.last.transactions

我基本上想办法找出设置的关联，所以我可以通过这样的基础上，在用户和角色之间的关系定义的角色抢夺用户的交易：

I am basically trying to figure out a way to setup an association so I can grab the user's transactions via something like this based on the roles defined in the association between the user and roles:

user = User.find(1)
transactions = user.transactions

我不知道这是否可能？我希望你明白我想要做的事情。

I am not sure if this is possible? I hope you understand what I am trying to do.

推荐答案

如果您不想执行单独的SQL查询来找到每个角色交易，你可以先拿到role_ids用户，然后找到所有交易这些角色ID单查询：

If you don't want to execute separate SQL queries to find transactions for each role, you can first get role_ids for the user, and then find all transactions with these role ids with single query:

class User < ActiveRecord::Base
  #...
  def transactions
    Transaction.scoped(:conditions => {:role_id => role_ids})
  end
end

Transaction.scoped 用在这里，因此您可以在必要时添加更多的条件，如

Transaction.scoped is used here so you can add more conditions when necessary, like

user.transactions.all(:limit => 10, :conditions => [ ... ])

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