I have the following in my application controller:
before_filter :set_current_subdomain
protected
def set_current_subdomain
Thread.current[:current_subdomain] = current_subdomain
#account = Account.find_by_subdomain(current_subdomain)
end
def current_subdomain
request.subdomain
end
and then the following in some of my models:
default_scope :conditions => { :account_id => (Thread.current[:account].id unless Thread.current[:account].nil?) }
Now, this works - some of the time. I for instance load up an index method and get back a list of records with the scope applied, but also sometimes get an empty list as Thread.current[:account_id] is coming out as nil, even though queries earlier in the request are working using the same value.
Question is, why is this not working, and is there a better way to set a variable that's global to the current request?
Manipulating the Thread local variables is a really bad idea and is going to lead to nothing but sadness, heartache, and pain. There's no guarantee that different parts of the request processing will be handled by the same thread, and because of this, your variables might end up getting lost.
The Rails convention is to create instance variables in the context of ApplicationController. In simple terms, all you really do is this:
class ApplicationController < ActionController::Base
before_filter :set_current_subdomain
attr_reader :current_subdomain
helper_method :current_subdomain
protected
def set_current_subdomain
#current_subdomain = request.subdomain
#account = Account.find_by_subdomain(#current_subdomain)
end
end
Any #... type variables you create will be attached to the instance of the ApplicationController associated with the current request. It's important to note that each request will be issued a brand-new instance of the appropriate controller class.
You're free to create whatever instance variables you want provided they don't somehow conflict with those used by Rails itself but in general terms this doesn't happen very often and conflicts typically occur on method names instead.
Class-level instance variables will persist between requests in environments where the "cache classes" flag is enabled. In the development environment your controller class is re-loaded each time a request is made to ensure it reflects the current state of your source files.
Related
I am facing an issue with accessing a particular variable of a method say A , in another method say B in the controller.. The size of the object(variable) is too big since it contains the results of a service call made.. My usecase is like on selecting an option from a drop down box, it redirects to a method B in controller and the same object(variable) should be parsed. How can I access the variable in the other method?
I tried storing in a cookie and since the size is too big I am getting Cookie Overflow exception. I am not using a DB. So I guess using memcache won't work. Also tried storing it as hidden field in view and passed its value as a data through ajax call. But I am getting it as a string. Tried to specify datatype as json and several other ways.. but of no use..Using ##var also din work..Not sure why..
Code:
On change of the drop down:
$(document).ready(function(){
$('#filter_service').change(function() {
$.ajax({type: "GET",
url: "/device_troubleshootings/query_operation",
data: { filter_service: $('# filter_service').val()},
});
});
});
Service call:
def log_results
//Service call
#get_log_results = LogQueryService.client.get_logs(Com::Amazon::Logqueryservice::DeviceSerialNumberQuery.new(:search_text => # search , :index => 'dms', :index_type => '_all', :from_time_stamp => #from_time_stamp, :to_time_stamp => #to_time_stamp))
#dsn_result = #get_log_results.logs_result_obj_list
end
Here, I am trying to access #dsn_result object in "/device_troubleshootings/query_operation” method.
Please suggest me ways to access the variable.
MVC
I think you're getting confused with how Rails should work
Remember, Rails (which is just a framework for Ruby) is built on the "MVC" programming pattern. This means each time you send a request to your Rails application, it has to be handled by a single controller#action which you will then allow you to pull the relevant data from your models
The problem you have is you're trying to load multiple controller methods, and pass the same data to both. This might work in Ruby, but not Rails (Rails is stateless):
--
Model
The correct way to handle this type of setup is by creating another request for your application, which will load another controller#action, allowing you to access the data you need
As demonstrated by the MVC diagram above, each time you send a request to Rails, it's basically a new request. This means that unless you've persisted your data in the likes of a cookie, you'll need to load the data from the model.
The problem you have is you're trying to store an entire data-set in the front-end of your system. This issue is very bad, as not only is it inefficient, but it goes against the MVC pattern completely.
You'll be much better storing the bare-minimum data set you need in the front-end (ids or similar), which you will then be able send to your controller via ajax; building a new data-set from
--
Class Variables
You mentioned you tried to declare some ##class variables to no avail. The problem with this is that the class vars will only be available for an instance of a class.
As mentioned, since Rails is stateless, the class variables won't persist between requests (how can they?). I think you know this already, considering you've been trying to use cookies to store your data
The way to resolve this is to rebuild the data each time from the model (as detailed above)
Solution
The solution for you is to "go stateless"
Here's how:
Treat Method A and Method B as completely separate "ACTIONS"
When using these actions, you need to consider the smallest piece of data to pass between the two
To load Method B, you need to send a new request from your browser (as if you've never loaded Method A before)
Your method_a can be handled in the "standard" way:
#config/routes.rb
resources :your_controller do
collection do
get :method_a
get :method_b
end
end
This will mean that you can load method_a relatively simply:
#app/controllers/your_controller.rb
Class YourController < ApplicationController
def method_a
#get_log_results = LogQueryService.client.get_logs(Com::Amazon::Logqueryservice::DeviceSerialNumberQuery.new(:search_text => # search , :index => 'dms', :index_type => '_all', :from_time_stamp => #from_time_stamp, :to_time_stamp => #to_time_stamp))
#dsn_result = #get_log_results.logs_result_obj_list
end
end
As you know, the #dsn_result will not persist through to the next request.
There are two ways to resolve this (set a CONSTANT -- if you're pulling from an API, this will give you a single call -- or use a before_action to set the variable for as many actions as you need). I'll detail both for you:
#app/controllers/your_controller.rb
Class YourController < ApplicationController
before_action :set_log_data
def method_a
end
def method_b
end
private
def set_log_data
#get_log_results = LogQueryService.client.get_logs(Com::Amazon::Logqueryservice::DeviceSerialNumberQuery.new(:search_text => # search , :index => 'dms', :index_type => '_all', :from_time_stamp => #from_time_stamp, :to_time_stamp => #to_time_stamp))
#dsn_result = #get_log_results.logs_result_obj_list
end
end
This will work if you pull data from your own data-set (using the models), however, the better way to do this in your case will likely be to set a constant (considering, of course, that you don't want the data to change):
#config/initializers/dsn_result.rb
get_log_results = LogQueryService.client.get_logs(Com::Amazon::Logqueryservice::DeviceSerialNumberQuery.new(:search_text => # search , :index => 'dms', :index_type => '_all', :from_time_stamp => #from_time_stamp, :to_time_stamp => #to_time_stamp))
DSN_RESULT = get_log_results.logs_result_obj_list
In my case I solved with global variable $my_global_var
So my files look like this
routes.rb
Rails.application.routes.draw do
resources :pages
root 'pages#index'
post 'pages/test'
end
pages_controller.rb
class PagesController < ApplicationController
def firstaction
$my_global_var = "My global var"
puts $my_global_var
end
def secondaction
puts $my_global_var
end
end
index.html.erb
<%= button_to 'Test', pages_test_path, method: :post %>
I'd like to use pg_audit_log for logging in a rails app. The audit log must not only show the columns that have changed, but also the user who made those changes. The docs don't show how to do this, but after looking through the pg_audit_log source (postgresql_adapter.rb) I see it reads user information from a thread local variable, ala:
current_user = Thread.current[:current_user]
I've considered setting/unsetting this in before and after filters like so:
Thread.current[:current_user] = current_user
(using the current_user helper method in the controller to get the currently logged in user), but that seems dangerous. I'm now spending time trying to understand how the rails request cycle and threads interact, to get a better feel for just how dangerous. In the mean time, I was curious if any SO users currently using pg_audit_log have solved the need to log the user_id and user_unique_name to the log tables each time the user makes a change to a record.
Setting the current user the way you describe is a common way to do it. See, for example, http://rails-bestpractices.com/posts/47-fetch-current-user-in-models
Some example code could look like:
# in your model
class User < ActiveRecord::Base
def self.current
Thread.current[:current_user]
end
def self.current=(user)
Thread.current[:current_user] = user if user.nil? || user.is_a?(User)
end
end
# in your controller
class ApplicationController < ActionController::Base
before_filter :set_current_user
def set_current_user
User.current = user_signed_in? ? current_user : nil
end
end
Relying on the Thread.current hash to provide model-level access to objects managed by the controller is indeed controversial. For example, see the following:
Safety of Thread.current[] usage in rails
It is worrisome that this particular feature is undocumented in the pg_audit_log gem.
Suppose you had not actively explored the gem's source code, and suppose you had independently decided to define Thread.current[:current_user] = something in your own application, for your own purpose. In that case, pg_audit_log would audit that object, without your knowledge.
Granted, the name current_user is so universally accepted to mean the currently logged-on user as defined by authentication routines that it's difficult to imagine this potential bug as a concrete problem, but from a design standpoint? Ouch.
On the other hand, since you know what you are doing, ensuring that Thread.current[:current_user] is set/unset at the beginning/end of each and every response cycle should make the process safe. At least that's what I gather from reading lots of posts on the topic.
Cheers, Giuseppe
I have to write a threaded Rails app because I am running it atop of Neo4j.rb, which embeds a Neo4j graph database inside the Rails process, and thus I have to serve multiple requests from the same process. Yeah, it'd be cool if connecting to a Neo4j database worked like SQL databases, but it doesn't, so I'll quit complaining and just use it.
I'm quite worried about the implications of writing concurrent code (as I should be), and just need some advice on how to handle common a common scenario - a controller sets an instance variable or a variable in the session hash, then some stuff happens. Consider the following crude code to demonstrate what I mean:
# THIS IS NOT REAL PRODUCTION CODE
# I don't do this in real life, it is just to help me ask my question, I
# know about one-way hashing, etc.!
class SessionsController
def create
user = User.find_by_email_and_password(params[:email], params[:password])
raise 'auth error' unless user
session[:current_user_id] = user.id
redirect_to :controller => 'current_user', :action => 'show'
end
end
class CurrentUserController
def show
#current_user = User.find(session[:current_user_id])
render :action => :show # .html.erb file that uses #current_user
end
end
The question: Are there any race conditions in this code?
In SessionsController, are the session hash and the params hash thread-local? Say the same browser session makes multiple requests to /sessions#create (to borrow Rails route syntax) with different credentials, the user that is logged in should be the request that hit the line session[:current_user_id] = user.id last? Or should I wrap a mutex lock around the controller action?
In the CurrentUserController, if the show action is hit simultaneously by two requests with different sessions, will the same #current_user variable be set by both? I.e. will the first request, as it is processing the .html.erb file, find that it's #current_user instance variable has suddenly been changed by the second thread?
Thanks
Each request gets a new instance of your controller. As a consequence controller instance variables are thread safe. params and session are also backed by controller instance variables (or the request object itself) and so are also safe.
It's important to know what is shared between threads and what isn't.
Now back to your specific example. Two requests hit CurrentUserController#show simultaneously, hence they are handled by two concurrent threads. The key here is that each thread has its own instance of CurrentUserController, so there are two #current_user variables which don't interfere. So there's no race condition around #current_user.
An example of race condition would be this:
class ApplicationController < ActionController::Base
before_each :set_current_user
cattr_accessor :current_user
def set_current_user
self.class.current_user = User.find_by_id(session[:current_user_id])
end
end
# model
class LogMessage < ActiveRecord::Base
belongs_to :user
def self.log_action(attrs)
log_message = new(attrs)
log_message.user = ApplicationController.current_user
log_message.save
end
end
On more general note, because of GIL (Global Interpreter Lock) benefits from using threads in MRI ruby are rather limited. There are implementation which are free from GIL (jruby).
I have a situation where I want to make a request to third-party API(url shortening service) after creating a record in the database (updates a column in the table which stores the short url), in order to decouple the API request from the Model, I have set up an ActiveRecord Observer which kicks in every time a record is created, using after_create callback hook, here is the relevant code:
class Article < ActiveRecord::Base
has_many :comments
end
class ArticleObserver < ActiveRecord::Observer
def after_create(model)
url = article_url(model)
# Make api request...
end
end
The problem in the above code is article_url because Rails Routes are not available in either Model or ModelObservers, same as ActionMailer (similar problem exists in Mails where if we need to put an URL we have to configure "ActionMailer::default_options_url"). In theory accessing routes/request object in Model is considered a bad design. To circumvent the above issue I could include the url_helpers module as described in the following URL:
http://slaive-prog.tumblr.com/post/7618787555/using-routes-in-your-model-in-rails-3-0-x
But this does not seem to me a clean solution, does anybody have a pointer on this issue or any advice on how it should be done?
Thanks in advance.
I would definitely not let your models know about your routes. Instead, add something like attr_accessor :unshortened_url on your Article class. Set that field in your controller, and then use it from your observer. This has the added benefit of continuing to work if you later decide to set your shortened URL asynchronously via a background task.
Edit
A couple of things, first of all.
Let's get the knowledge of creating a short_url out of the model
entirely.
We could nitpick and say that the short_url itself doesn't belong in the model at all, but to remain practical let's leave it in there.
So let's move the trigger of this soon-to-be-background task into the controller.
class ArticlesController < ApplicationController
after_filter :short_url_job, :only => [:create]
# ...
protected
def short_url_job
begin
#article.short_url = "I have a short URL"
#article.save!
rescue Exception => e
# Log thy exception here
end
end
end
Now, obviously, this version of short_url_job is stupid, but it illustrates the point. You could trigger a DelayedJob, some sort of resque task, or whatever at this point, and your controller will carry on from here.
I have a variable that I need globally available throughout my app (so I've set #account in the applicationController).
However, a plugin that I have needs access to the same variable.
Note: This variable is distinct on each request.
What is the best way of creating this architecture?
Maybe something like this will work:
class Account
def self.current
#current
# or: Thread.current[:current_account]
end
def self.current=(a)
#current = a
# or: Thread.current[:current_account] = a # ..if you want to be thread-safe.
end
...
end
# your controller's before_filter:
def assign_account
...
Account.current = #account # But remember to set nil if none found!
end
# Any code in your app (view, model, almost anything):
<%= Account.current.name if Account.current %>
Setting #account in your app controller doesn't make it globally available throughout the app - models can't access it for example. Any instance var set in the controller will be available only in the controller or views. If the plugins have controller and view code then this code should be able to access the variable in the normal way, as long as the variable is set before the plugin controller code runs for example.
If you provide more details about what you want to do (ie where/how you want to access #account) then someone may be able to suggest a good approach.