before_filter :require_owner

我有许多资源（行程、时间表等），其操作应仅限于资源所有者。

如何使用 ApplicationController 中定义的 #require_owner 方法来实现代码来实现此目的？理想情况下，代码将查找所有者的继承链，以便 before_filter 将处理属于_to :trip 的 :comment 和属于_to :user。

class TripsController < ApplicationController
  belongs_to :member
  before_filter :require_owner

  ...

end

我没有完全遵循描述（评论真的属于旅行所有者吗？），但稍微扩展一下 jonnii 的答案，这里是一个限制旅行控制器的示例：

class ApplicationController < ActionController::Base
  ...
protected
  # relies on the presence of an instance variable named after the controller
  def require_owner
    object = instance_variable_get("@#{self.controller_name.singularize}")
    unless current_user && object.is_owned_by?(current_user)
      resond_to do |format|
        format.html { render :text => "Not Allowed", :status => :forbidden }
      end
    end
  end
end

class TripsController < ApplicationController
  before_filter :login_required # using restful_authentication, for example
  # only require these filters for actions that act on single resources
  before_filter :get_trip, :only => [:show, :edit, :update, :destroy]
  before_filter :require_owner, :only => [:show, :edit, :update, :destroy]
  ...
protected
  def get_trip
    @trip = Trip.find(params[:id])
  end
end

假设模型如下所示：

class Trip < ActiveRecord::Base
    belongs_to :owner, :class_name => 'User'
    ...
    def is_owned_by?(agent)
      self.owner == agent
      # or, if you can safely assume the agent is always a User, you can 
      # avoid the additional user query:
      # self.owner_id == agent.id
    end
end

The login_required方法（由restful_authentication或authlogic等auth插件提供或依赖）确保用户已登录并为用户提供current_user方法，get_trip设置随后检入的行程实例变量require_owner.

只要该模型已实现is_owned_by?方法。如果您在资源是评论时尝试检查它，那么您将处于CommentsController:

class CommentsController < ApplicationController
  before_filter :login_required # using restful_authentication, for example
  before_filter :get_comment, :only => [:show, :edit, :update, :destroy]
  before_filter :require_owner, :only => [:show, :edit, :update, :destroy]

  ...
protected
  def get_comment
    @comment = Comment.find(params[:id])
  end
end

with a Comment模型看起来像：

class Comment < ActiveRecord::Base
  belongs_to :trip

  # either 
  #  delegate :is_owned_by?, :to => :trip
  # or the long way:
  def is_owned_by?(agent)
    self.trip.is_owned_by?(agent)
  end
end

确保在执行此操作时检查日志，因为如果您不小心，依赖于关联的检查可能会导致大量查询。