Owner-filtered model objects on Rails 3

问题:

I need to do some filtering on my ActiveRecord models, I want to filter all my model objects by owner_id. The thing I need is basically the default_scope for ActiveRecord.

But I need to filter by a session variable, which is not accessible from the model. I've read some solutions, but none works, basically any of them says that you can use session when declaring default_scope.

This is my declaration for the scope:

class MyModel < ActiveRecord::Base
    default_scope { where(:owner_id => session[:user_id]) }
    ...
end

Simple, right?. But it fails saying that method session does not exists.

Hope you can help

回答1:

Session objects in the Model are considered bad practice, instead you should add a class attribute to the User class, which you set in an around_filter in your ApplicationController, based on the current_user

class User < ActiveRecord::Base

    #same as below, but not thread safe
    cattr_accessible :current_id

    #OR

    #this is thread safe
    def self.current_id=(id)
      Thread.current[:client_id] = id
    end

    def self.current_id
      Thread.current[:client_id]
    end  

end

and in your ApplicationController do:

class ApplicationController < ActionController::Base
    around_filter :scope_current_user  

    def :scope_current_user
        User.current_id = current_user.id
    yield
    ensure
        #avoids issues when an exception is raised, to clear the current_id
        User.current_id = nil       
    end
end

And now in your MyModel you can do the following:

default_scope where( owner_id: User.current_id ) #notice you access the current_id as a class attribute

回答2:

You will not be able to incorporate this into a default_scope. This would break every usage within (e.g.) the console as there is no session.

What you could do: Add a method do your ApplicationController like this

class ApplicationController
  ...
  def my_models
    Model.where(:owner_id => session[:user_id])
  end
  ...

  # Optional, for usage within your views:
  helper_method :my_models
end

This method will return a scope anyhow.

回答3:

Session related filtering is a UI task, so it has its place in the controller. (The model classes do not have access to the request cycle, session, cookies, etc).

What you want is

# my_model_controller.rb
before_filter :retrieve_owner_my_models, only => [:index] # action names which need this filtered retrieval

def retrieve_owner_my_models
   @my_models ||=  MyModel.where(:owner_id => session[:user_id])
end

Since filtering by ownership of current user is a typical scenario, maybe you could consider using standard solutions, like search 'cancan gem, accessible_by'

Also be aware of the evils of default_scope. rails3 default_scope, and default column value in migration