Rails 3：如何编写 DRYer 范围

发布于 2024-11-06 15:36:50 字数 808 浏览 0 评论 0原文

我发现自己在两个地方编写非常相似的代码，一次是在模型上定义（虚拟）布尔属性，一次是定义范围以查找与该条件匹配的记录。本质上，

scope :something, where(some_complex_conditions)

def something?
  some_complex_conditions
end

一个简单的例子：我正在为俱乐部会员资格建模； 会员支付费用，该费用仅在特定年份有效。

class Member < ActiveRecord::Base
  has_many :payments
  has_many :fees, :through => :payments

  scope :current, joins(:fees).merge(Fee.current)

  def current?
    fees.current.exists?
  end
end

class Fee < ActiveRecord::Base
  has_many :payments
  has_many :members, :through => :payments

  scope :current, where(:year => Time.now.year)

  def current?
    year == Time.now.year
  end
end

是否有一种更干燥的方法来编写使用虚拟属性的范围（或者，确定模型是否与范围的条件匹配）？

我对 Rails 还很陌生，所以请指出我是否做了一些愚蠢的事情！

原文

I'm finding myself writing very similar code in two places, once to define a (virtual) boolean attribute on a model, and once to define a scope to find records that match that condition. In essence,

scope :something, where(some_complex_conditions)

def something?
  some_complex_conditions
end

A simple example: I'm modelling a club membership; a Member pays a Fee, which is valid only in a certain year.

class Member < ActiveRecord::Base
  has_many :payments
  has_many :fees, :through => :payments

  scope :current, joins(:fees).merge(Fee.current)

  def current?
    fees.current.exists?
  end
end

class Fee < ActiveRecord::Base
  has_many :payments
  has_many :members, :through => :payments

  scope :current, where(:year => Time.now.year)

  def current?
    year == Time.now.year
  end
end

Is there a DRYer way to write a scopes that make use of virtual attributes (or, alternatively, to determine whether a model is matched by the conditions of a scope)?

I'm pretty new to Rails so please do point out if I'm doing something stupid!

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凡间太子 2024-11-13 15:36:50

这不是问题的答案，但您的代码有一个错误（如果您在生产中使用类似的东西）：Time.now.year 将返回服务器启动的年份。您希望在 lambda 中运行此范围以使其按预期运行。

scope :current, lambda { where(:year => Time.now.year) }

This in not an answer to the question, but your code has a bug (in case you use something similar in production): Time.now.year will return the year the server was started. You want to run this scope in a lambda to have it behave as expected.

scope :current, lambda { where(:year => Time.now.year) }

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过度放纵 2024-11-13 15:36:50

不，没有更好的方法来完成您想要做的事情（除了注意 Geraud 的评论）。在您的范围内，您定义一个类级过滤器，它将生成用于限制查找器返回的结果的 SQL，在您定义要在此类的特定实例上运行的实例级测试的属性中。

是的，代码是相似的，但它在不同的上下文中执行不同的功能。

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内心旳酸楚 2024-11-13 15:36:50

是的，您可以在作用域中使用一个或多个带有 lambda 的参数。假设您有一组物品，并且您想要取回“Boot”或“Helmet”：

  scope :item_type, lambda { |item_type|
    where("game_items.item_type = ?", item_type )
  }

您现在可以执行 game_item.item_type('Boot') 来仅获取靴子或 game_item.item_type('头盔'）只获得头盔。这同样适用于你的情况。您可以在作用域中只包含一个参数，以便以一种更干燥的方式检查同一作用域上的一个或多个条件。

Yes, you can use one or more parameters with a lambda in your scopes. Suppose that you have a set of items, and you want to get back those that are either 'Boot' or 'Helmet' :

  scope :item_type, lambda { |item_type|
    where("game_items.item_type = ?", item_type )
  }

You can now do game_item.item_type('Boot') to get only the boots or game_item.item_type('Helmet') to get only the helmets. The same applies in your case. You can just have a parameter in your scope, in order to check one or more conditions on the same scope, in a DRYer way.

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