如何在Rails 3的范围ActiveRecord关联？ [英] How do you scope ActiveRecord associations in Rails 3?

问题描述

我有一个Rails 3的项目。使用Rails 3来阿雷尔和重用一个作用域再建的能力。我想知道如果有一种方法，当定义关系（如的has_many）使用范围。

我有权限列记录。我想建立一个default_scope这需要我的允许列考虑到这样的记录（即使是通过关系进入）进行过滤。

presently，在Rails 3中，default_scope（包括补丁我发现）不提供通过一个进程（这是我需要的后期变量绑定）的可行手段。是否有可能定义一个的has_many成一个命名范围，可以通过？

重用一个名为范围会是什么样子的想法：

  Orders.scope：my_orders，拉姆达{其中（：user_ID的=＆GT; User.current_user.id）}
的has_many：订单：范围=＆GT; Orders.my_orders
 

或暗示的编码名为范围的关系将是这样的：

 的has_many：订单：范围=＆GT;拉姆达{其中（：user_ID的=＆GT; User.current_user.id）}
 

我只是尝试应用default_scope与后期绑定。我将preFER使用阿雷尔方法（如果有的话），但将使用任何可行的选项。

由于我这里指的是当前用户，我可以不依赖于没有在最后一刻被评估条件，如：

 的has_many：订单：条件=＆GT; [user_ID的=？，User.current_user.id]
 

解决方案

我建议你看一看的命名范围都死了

作者解释有阿雷尔多么强大：）

我希望能对大家有所帮助。

编辑＃2014年3月1日

由于一些国家的意见，不同的是，现在的个人喜好问题。

不过，我还是个人建议，以避免暴露阿雷尔的范围，上层（该控制器或其他任何直接访问模式），而且这样做会要求：

1. 创建一个范围，将其暴露在直通模型的方法。该方法将是一个你接触到的控制器;
2. 如果你从来没有暴露你的模型，你的控制器（让你有一些在它们之上的服务层），那么你的罚款。反腐败层的是的为您服务，它可以访问你的模型的范围，而不用担心太多有关如何作用域实现的。

I have a Rails 3 project. With Rails 3 came Arel and the ability to reuse one scope to build another. I am wondering if there is a way to use scopes when defining a relationship (e.g. a "has_many").

I have records which have permission columns. I would like to build a default_scope that takes my permission columns into consideration so that records (even those accessed through a relationship) are filtered.

Presently, in Rails 3, default_scope (including patches I've found) don't provide a workable means of passing a proc (which I need for late variable binding). Is it possible to define a has_many into which a named scope can be passed?

The idea of reusing a named scope would look like:

Orders.scope :my_orders, lambda{where(:user_id => User.current_user.id)}
has_many :orders, :scope => Orders.my_orders

Or implicitly coding that named scope in the relationship would look like:

has_many :orders, :scope => lambda{where(:user_id => User.current_user.id)}

I'm simply trying to apply default_scope with late binding. I would prefer to use an Arel approach (if there is one), but would use any workable option.

Since I am referring to the current user, I cannot rely on conditions that aren't evaluated at the last possible moment, such as:

has_many :orders, :conditions => ["user_id = ?", User.current_user.id]

解决方案

I suggest you take a look at "Named scopes are dead"

The author explains there how powerful Arel is :)

I hope it'll help.

EDIT #1 March 2014

As some comments state, the difference is now a matter of personal taste.

However, I still personally recommend to avoid exposing Arel's scope to an upper layer (being a controller or anything else that access the models directly), and doing so would require:

1. Create a scope, and expose it thru a method in your model. That method would be the one you expose to the controller;
2. If you never expose your models to your controllers (so you have some kind of service layer on top of them), then you're fine. The anti-corruption layer is your service and it can access your model's scope without worrying too much about how scopes are implemented.

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