How to call expire_fragment from Rails Observer/Model? - ruby-on-rails

I've pretty much tried everything, but it seems impossible to use
expire_fragment from models? I know you're not supposed to and it's
non-MVC, but surely there much be some way to do it.
I created a module in lib/cache_helper.rb with all my expire helpers,
within each are just a bunch of expire_fragment calls. I have all my
cache sweepers setup under /app/sweepers and have an "include
CacheHelper" in my application controller so expiring cache within the
app when called via controllers works fine.
Then things is I have some external daemons and especially some
recurring cron tasks which call a rake task that calls a certain
method. This method does some processing and inputs entries into the
model, after which I need to expire cache.
What's the best way to do this as I can't specify cache sweeper within the model.
Straight up observers seem to be the best solution but then it
complains about expire_fragment being undefined etc etc, I've even
tried including the ActionController caching classes into the observer
but that didn't work. I'd love some ideas of how to create a solution
for this. Thanks.

Disclaimer: My rails is a bit rusty, but this or something like it should work
ActionController::Base.new.expire_fragment(key, options = nil)

The solution provided by Orion works perfectly. As an enhancement and for convenience, I've put the following code into config/initializers/active_record_expire_fragment.rb
class ActiveRecord::Base
def expire_fragment(*args)
ActionController::Base.new.expire_fragment(*args)
end
end
Now, you can use expire_fragment on all instances of ActiveRecord::Base, e.g. User.first.expire_fragment('user-stats')

This is quite easy to do. You can implement Orion's suggestion, but you can also implement the broader technique illustrated below, which gives you access to the current controller from any model and for whichever purpose you decided to break MVC separation for (e.g. messing with the fragment cache, accessing current_user, generating paths/URLs, etc.)
In order to gain access to the current request's controller (if any) from any model, add the following to environment.rb or, much preferably, to a new plugin (e.g. create vendor/plugins/controller_from_model/init.rb containing the code below):
module ActiveRecord
class Base
protected
def self.thread_safe_current_controller #:nodoc:
Thread.current[:current_controller]
end
def self.thread_safe_current_controller=(controller) #:nodoc:
Thread.current[:current_controller] = controller
end
# pick up the correct current_controller version
# from ##allow_concurrency
if ##allow_concurrency
alias_method :current_controller, :thread_safe_current_controller
alias_method :current_controller=, :thread_safe_current_controller=
else
cattr_accessor :current_controller
end
end
end
Then, in app/controllers/application.rb,
class ApplicationController < ActionController::Base
before_filter { |controller|
# all models in this thread/process refer to this controller
# while processing this request
ActiveRecord::Base.current_controller = controller
}
...
Then, from any model,
if controller = ActiveRecord::Base.current_controller
# called from within a user request
else
# no controller is available, didn't get here from a request - maybe irb?
fi
Anyhow, in your particular case you might want to inject code into your various ActiveRecord::Base descendants when the relevant controller classes load, so that the actual controller-aware code still resides in app/controllers/*.rb, but it is not mandatory to do so in order to get something functional (though ugly and hard to maintain.)
Have fun!

In one of my scripts I use the following hack:
require 'action_controller/test_process'
sweepers = [ApartmentSweeper]
ActiveRecord::Base.observers = sweepers
ActiveRecord::Base.instantiate_observers
controller = ActionController::Base.new
controller.request = ActionController::TestRequest.new
controller.instance_eval do
#url = ActionController::UrlRewriter.new(request, {})
end
sweepers.each do |sweeper|
sweeper.instance.controller = controller
end
Then, once the ActiveRecord callbacks are called, sweepers are able to call expire_fragment.

I'm a bit of a rails noob, so this may not be correct, or even helpful, but it seems wrong to be trying to call controller actions from within the model.
Is it not possible to write an action within the controller that does what you want and then invoke the controller action from within your rake task?

Why not have your external rake tasks call the expiry method on the controller. Then you're still being MVC compliant, you aren't building in a dependence on some scoping hack, etc.
For that matter, why don't you just put all the daemon / external functionality on a controller and have rake / cron just call that. It would be loads easier to maintain.
-- MarkusQ

Will it not be easier and clean just to pass the current controller as an argument to the model method call? Like following:
def delete_cascade(controller)
self.categories.each do |c|
c.delete_cascade(controller)
controller.expire_fragment(%r{article_manager/list/#{c.id}.*})
end
PtSection.delete(self.id)
controller.expire_fragment(%r{category_manager/list/#{self.id}.*})
end
You can access all public methods and properties of the controller from within model.
As long as you do not modify the state of the controller, it should be fine.

This might not work for what you're doing, but you may be able to define a custom call back on your model:
class SomeModel < ActiveRecord::Base
define_callback :after_exploded
def explode
... do something that invalidates your cache ...
callback :after_exploded
end
end
You can then use a sweeper like you would normally:
class SomeModelSweeper < ActionController::Caching::Sweeper
observe SomeModel
def after_exploded(model)
... expire your cache
end
end
Let me know if this is useful!

Related

Rails: How to POST internally to another controller action?

This is going to sound strange, but hear me out...I need to be able to make the equivalent of a POST request to one of my other controllers. The SimpleController is basically a simplified version of a more verbose controller. How can I do this appropriately?
class VerboseController < ApplicationController
def create
# lots of required params
end
end
class SimpleController < ApplicationController
def create
# prepare the params required for VerboseController.create
# now call the VerboseController.create with the new params
end
end
Maybe I am over-thinking this, but I don't know how to do this.
Inter-controller communication in a Rails app (or any web app following the same model-adapter-view pattern for that matter) is something you should actively avoid. When you are tempted to do so consider it a sign that you are fighting the patterns and framework your app is built on and that you are relying on logic has been implemented at the wrong layer of your application.
As #ismaelga suggested in a comment; both controllers should invoke some common component to handle this shared behavior and keep your controllers "skinny". In Rails that's often a method on a model object, especially for the sort of creation behavior you seem to be worried about in this case.
You shouldn't be doing this. Are you creating a model? Then having two class methods on the model would be much better. It also separates the code much better. Then you can use the methods not only in controllers but also background jobs (etc.) in the future.
For example if you're creating a Person:
class VerboseController < ApplicationController
def create
Person.verbose_create(params)
end
end
class SimpleController < ApplicationController
def create
Person.simple_create(params)
end
end
Then in the Person-model you could go like this:
class Person
def self.verbose_create(options)
# ... do the creating stuff here
end
def self.simple_create(options)
# Prepare the options as you were trying to do in the controller...
prepared_options = options.merge(some: "option")
# ... and pass them to the verbose_create method
verbose_create(prepared_options)
end
end
I hope this can help a little. :-)

Rails convention for method in multiple controllers

I have an app that has users whose profiles are accessible via site.com/username. When choosing a username, I make an AJAX call to a method in my UsersController to make sure the username is available (and check on the back end as well when submitted). I now want to add groups that will also be accessible through site.com/groupname. Since group and user names cannot collide, whatever controller method that responds to the AJAX call will need to check both so the check_username_available and check_groupname_available methods will do the exact same thing. What's the best practice / Rails way to handle this since I don't want to replicate code in both UsersController and GroupsController?
Having a method for each controller seems a bit redundant, even if the functionality is pulled out to a helper, since there will still be two routes that do the same thing. Having a separate controller solves the problem too but not sure this is good Rails practice.
code that is reused can be shared via a module
class UsersController < ActionController::Base
include NameUniqueness
end
class GroupsController < ActionController::Base
include NameUniqueness
end
module NameUniqueness
protected
def check_name
# implementation here
end
end
both controllers will now have access the check_name instance method.
DanPickett's answer is great.
Another choice is to make a class method in the user model and just call it from each controller. Since this name checking seems like a job for the model, that's what I would do.
class User
def self.check(stuff) ...

Ruby on Rails - Access controller variable from model

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
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
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]
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
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?
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.

Tracking model changes in Rails, automatically

In my rails app I would like to track who changes my model and update a field on the model's table to reflect.
So, for example we have:
class Foo < ActiveRecord::Base
before_create :set_creator
belongs_to :creator, :class_name => "User"
protected
def set_creator
# no access to session[:user_id] here...
end
end
What's a good testable way for me to get at the user_id from my model? Should I be wacking this data in Thread.current ?
Is it a better practice to hand this information from the controller?
Best practice in MVC is to have your Models be stateless, the controller gets to handle state. If you want the information to get to your models, you need to pass it from the controller. Using a creation hook here isn't really the right way to go, because you are trying to add stateful data, and those hooks are really for stateless behavior.
You can pass the info in from the controller:
Foo.new(params[:foo].merge {:creator_id => current_user.id})
Or you can create methods on User to handle these operations:
class User
def create_foo(params)
Foo.new(params.merge! {:creator_id => self.id})
end
end
If you find yourself writing a lot of permissions code in the controller, I'd go with option 2, since it will let you refactor that code to the model. Otherwise option 1 is cleaner.
Omar points out that it's trickier to automate, but it can still be done. Here's one way, using the create_something instance method on user:
def method_missing(method_sym, *arguments, &block)
meth = method_sym.to_s
if meth[0..6] == "create_"
obj = meth[7..-1].classify.constantize.new(*arguments)
obj.creator_id = self.id
else
super
end
end
You could also override the constructor to require user_ids on construction, or create a method inside ApplicationController that wraps new.
There's probably a more elegant way to do things, but I definitely don't like trying to read state from inside Model code, it breaks MVC encapsulation. I much prefer to pass it in explicitly, one way or another.
Yeah, something like that would work, or having a class variable on your User model
cattr_accessor :current_user
Then in your controller you could have something like:
User.current_user = current_user
inside a before filter (assuming current_user is the logged in user).
You could then extend AR:Base's create/update methods to check for the existence of a created_by/updated_by field on models and set the value to User.current_user.
I'd create new save, update, etc methods that take the user_id from everything that calls them (mainly the controller).
I'd probably extend ActiveRecord:Base into a new class that handles this for all the models that need this behaviour.
I wouldn't trust Thread.current, seems a bit hackish. I would always call a custom method which takes an argument:
def create_with_creator(creator, attributes={})
r = new(attributes)
r.creator = creator
r.save
end
As it follows the MVC pattern. The obviously inherient problem with this is that you're going to be calling create_with_creator everywhere.
You might find PaperTrail useful.
Probably you could check out usertamp plugins, found two in github
http://github.com/delynn/userstamp/tree/master
http://github.com/jnunemaker/user_stamp/tree/master

Rails: macro style functions

In models and controllers, we often use Rails macros like before_validation, skip_before_filter on top of the class definition.
How is this implemented? How do I add custom ones?
Thanks!
They're just standard Ruby functions. Ruby's flexible approach to syntax makes it look better than it is. You can create your own simply by writing your method as a normal Ruby function and doing one of the following:
putting it somewhere that's accessible by your controllers such as application.rb
putting it in a file and requiring it in.
mixing the code into a class via the Ruby include keyword.
That last option is great for model classes and the first option is really only for controllers.
An Example
An example of the first approach is shown below. In this example we add code into the ApplicationController class (in application.rb) and use it in the other controllers.
class BusinessEntitiesController < ApplicationController
nested_within :Glossary
private
# Standard controller code here ....
The nested_within provides helper functions and variables to help identify the id of the "parent" resource. In effect it parses the URL on the fly and is accessible by every one of our controllers. For example when a request comes into the controller, it is automatically parsed and the class attribute #parent_resource is set to the result of a Rails find. A side effect is that a "Not Found" response is sent back if the parent resource doesn't exist. That saves us from typing boiler plate code in every nested resource.
That all sounds pretty clever but it is just a standard Ruby function at heart ...
def self.nested_within(resource)
#
# Add a filter to the about-to-be-created method find_parent_id
#
before_filter :find_parent_id
#
# Work out what the names of things
#
resource_name = "#{resource.to_s.tableize.singularize}"
resource_id = "#{resource_name}_id"
resource_path = "#{resource.to_s.tableize}_path"
#
# Get a reference to the find method in the model layer
#
finder = instance_eval("#{resource}.method :find_#{resource_name}")
#
# Create a new method which gets executed by the before_filter above
#
define_method(:find_parent_id) do
#parent_resource = finder.call(params[resource_id])
head :status => :not_found, :location => resource_path
unless #parent_resource
end
end
The nested_within function is defined in ApplicationController (controllers/application.rb) and therefore gets pulled in automatically.
Note that nested_within gets executed inside the body of the controller class. This adds the method find_parent_id to the controller.
Summary
A combination of Ruby's flexible syntax and Rail's convention-over-configuration makes this all look more powerful (or weirder) than it actually is.
Next time you find a cool method, just stick a breakpoint in front of it and trace through it. Ahh Open Source!
Let me know if I can help further or if you want some pointers on how that nested_within code works.
Chris
Chris's answer is right. But here's where you want to throw your code to write your own:
The easiest way to add Controller methods like that is to define it in ApplicationController:
class ApplicationController < ActionController::Base
...
def self.acts_as_awesome
do_awesome_things
end
end
Then you can access it from individual controllers like so:
class AwesomeController < ApplicationController
acts_as_awesome
end
For models, you want to reopen ActiveRecord::Base:
module ActiveRecord
class Base
def self.acts_as_super_awesome
do_more_awesome_stuff
end
end
end
I personally would put that in a file in config/initializers so that it gets loaded once, and so that I know where to look for it always.
Then you can access it in models like so:
class MySuperAwesomeModel < ActiveRecord::Base
acts_as_super_awesome
end

Resources