ActiveRecord的发现通过协会 [英] activerecord find through association

问题描述

我尝试从我的分贝一个ActiveRecord对象。我的模型

I am trying to retrieve an activerecord object from my db. My models are

class User < ActiveRecord::Base
   belongs_to :account
   has_many :domains, :through => :account    
end

和

class Account < ActiveRecord::Base
   has_many :domains
   has_many :users
end

和

class Domain < ActiveRecord::Base
   belongs_to :account
end

现在我想获取基于用户名和域名用户（让我们假设这些都是用户的属性和领域类分别）。即沿东西的行

Now I would like to retrieve a user based on the username and a domain name (lets assume that these are attributes of the User and the Domain classes respectively). i.e. something along the lines of

User.find(:first, :conditions =>{:username => "Paul", :domains => { :name => "pauls-domain"}})

我知道，上面那块code将无法工作，因为我不得不提到一些有关的域的表。此外，用户和域之间的关联是一对多的（这可能进一步复杂的事情）。

I know that the above piece of code will not work since I do have to mention something about the domains table. Also, the association between users and domains is a one-to-many (which probably further complicates things).

如何任何想法应该这个查询中形成的呢？

Any ideas on how should this query be formed?

推荐答案

如果你使用的Rails 3.x中，以下code将得到查询结果：

If you're using Rails 3.x, the following code would get the query result:

User.where(:username => "Paul").includes(:domains).where("domains.name" => "paul-domain").limit(1)

要检查什么发生，可以追加 .to_sql 上面code。

To inspect what happen, you can append .to_sql to above code.

如果你使用Rails的2.X，你最好写的原始的SQL查询。

If you're using Rails 2.x, you'd better write the raw sql query.

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