如何在 Active Record 中加入 has_many 关联和范围？

Question

这是我的关联和范围设置：

has_many    :owned_products

has_many    :owned_lessons, :through => :owned_products, :source => :lesson, :conditions => "owned_products.product_type = 'Lesson'"

scope :active_purchase_scope, lambda {
    where('owned_products.created_at' => (Date.today - CONFIG['downloads']['time_window'].days)..(Date.today)).order('owned_products.created_at DESC')
}

def active_lessons 
    owned_lessons.active_purchase_scope
end

这是我得到的错误：

ruby-1.8.7-p334 :005 > User.find_by_username('joeblow').active_lessons
NoMethodError: undefined method `active_purchase_scope' for #<User:0x1051a26c8>

大

Answer 1

scope 可以被视为类方法，association 可以被视为实例方法。在您的代码示例中，owned_lessons 方法返回一个数组对象。您不能在数组对象（或用户对象）上调用 active_purchase_scope，因为范围只能在 Model 类上调用（即在您的情况下为 User.active_purchase_scope）

您可以通过在 Lesson 模型上添加范围来解决此问题

class Lesson
  has_many    :owned_products

  scope :active_purchase_scope, lambda {
    include(::owned_products).where('owned_products.created_at' => 
          (Date.today - CONFIG['downloads']['time_window'].days)..(Date.today)).
            order('owned_products.created_at DESC')
  }

end

并重写User类如下：

class User

  has_many    :owned_products

  has_many    :owned_lessons, :through => :owned_products, :source => :lesson, 
                 :conditions => "owned_products.product_type = 'Lesson'"


  def active_lessons 
    owned_lessons.active_purchase_scope
  end

end

owned_lessons 在Lesson 模型上返回一个匿名作用域，因此我们可以将它与来自同一模型的作用域active_purchase_scope 链接起来。