Ruby on Rails - Access controller variable from mo

问题:

I am trying to access an instance variable which is set in the controller in the model. The controller is the products controller and the model is the products model. The instance variable is a instance of another model called account.

The instance variable is @current_account

When I run the code nothing happens, I do not get an error. Does anyone know where I can find something read about access instance variables set in the controller from the model?

Thanks

Eef

回答1:

You shouldn't generally try to access the controller from the model for high-minded issues I won't go into.

I solved a similar problem like so:

class Account < ActiveRecord::Base
  cattr_accessor :current
end

class ApplicationController < ActionController::Base
  before_filter :set_current_account
  def set_current_account
    #  set @current_account from session data here
    Account.current = @current_account
  end
end

Then just access the current account with Account.current

回答2:

DISCLAIMER: The following code breaks MVC conventions, that said...

Using class attributes can probably lead to thread safety issues. I would use Thread.current + around_filter to store controller related data at thread level, and ensure it gets cleared just before the request finishes:

class ApplicationController < ActionController::Base

  around_filter :wrap_with_hack

  def wrap_with_hack
    # We could do this (greener solution): 
    # http://coderrr.wordpress.com/2008/04/10/lets-stop-polluting-the-threadcurrent-hash/
    # ... but for simplicity sake:
    Thread.current[:controller] = self
    begin
      yield
    ensure
     # Prevent cross request access if thread is reused later
     Thread.current[:controller] = nil
    end
  end
end

Now the current controller instance will be avaliable globaly during the request processing through Thread.current[:controller]

回答3:

If you need to access a controller variable from a model it generally means your design is wrong because a controller serves as bridge between view and model (at least in Rails), controller gets info from models, models shouldn't know anything about controllers, but if you want to do it anyway you can do it just as jeem said, but I'd rather do:

 class << self

    attr_accessor :current

 end

instead of

cattr_accessor :current

you can see why here => cattr_accessor doesn't work as it should

回答4:

I can't comment directly so I'll post here: the accepted answer does not seem to be right. As @vise notes, class variables are shared across requests. So unless there's just one current account for the entire app, this won't behave as expected.

For more, see the accepted answer by @molf here: Is Rails shared-nothing or can separate requests access the same runtime variables?

回答5:

I'm not sure if I understand the question exactly, but I'll take a stab.

I think if you need to access a controller instance variable from the model then you either need to make it an attribute in the model, or move your logic to the other class controller, not model.