Accessing object everywhere in rails app - ruby-on-rails

I know this is 1001st question about global objects, but I think my situation is slightly different.
I'm working on ecommerce solution, which provides few different shops within a single rails application.
There is a class Shop which provides shop-specific logic and options. For example:
#shop.tax should be accessible in models. Tax can differ depend on shop. eg 9%, 18%.
#shop.name and #shop.layout should be accessible in controllers and views.
#shop.email.general for mailers.
I need to be able to create an instance of Shop in application controller and somehow pass it to the all application parts.
# controllers/application_controller.rb
class ApplicationController < ActionController::Base
before_filter :set_shop
protected
def set_shop
requested_shop = if request.domain.match(/^.*shop1\.com$/)
:shop_1
elsif request.domain.match(/^.*shop2\.com$/)
:shop_2
end
#shop = Shop.new(requested_shop)
end
end
I know that request-based logic should not be used in models, but I really need shop options there. In tests I could mock this "global" object like that Shop.new(:test_shop) in spec_helper.
Is global variable my only choice? I've never used them.
I tried to use Settingslogic gem, but it defines attr_accessors for shop-specific options, and they persist between requests, which is not what I need.

One way of doing this would be something like
class Shop
def self.current=(shop)
Thread.current[:current_shop] = shop
end
def self.current
Thread.current[:current_shop]
end
end
Which allows you to maintain a separate current shop for each request.
The alternative is to pass the current shop around. It may seem tedious at first but can ultimately be simpler to reason about than global or pseudo global behaviour

Related

Repository or Gateway pattern in Ruby

How can I implement the Repository or Gateway pattern in Ruby?
I come from a C# world and I usually abstract away my data access but with ActiveRecord as the default data access mechanism in Ruby, it's not obvious how to accomplish that.
What I usually would do in C# is work with abstract interfaces and then have a concrete implementation for EFCustomerRepository, NHibernateCustomerRepository and InMemoryCustomerRepository and depending on the situation I inject the matching concrete implementation.
So now, what’s the Ruby way?!
As far as I understand it, in dynamic languages you would not need something like DI (dependency injection).
And Ruby has powerful language features to allow things like mixins.
But you would define the mixin to use statically on class or module-level?
How do I write my business logic if I want to develop against an in-memory repository and in production I would switch to my ActiveRecord-Repository?
If might be on the wrong path here since I'm used to thinking in a statically typed language. How would someone tackle this task the Ruby way? Basically I want to make my persistence layer abstract and it's implementations interchangeable.
EDIT: I am referring to robert c. martins (unclebob) keynote about architecture
Thanks for any help...
I get what you are saying. I come from a .NET background as well. Abstracting away your business logic & persistance logic is imo a good idea. I haven't found a gem that does it for you yet. But you can easily roll something simple yourself. In the end a repository pattern is basically a class that delegates to your persistance layer.
Here is what I do:
require 'active_support/core_ext/module/attribute_accessors'
class GenericRepository
def initialize(options = {})
#scope = options[:scope]
#association_name = options[:association_name]
end
def self.set_model(model, options = {})
cattr_accessor :model
self.model = model
end
def update(record, attributes)
check_record_matches(record)
record.update_attributes!(attributes)
end
def save(record)
check_record_matches(record)
record.save
end
def destroy(record)
check_record_matches(record)
record.destroy
end
def find_by_id(id)
scoped_model.find(id)
end
def all
scoped_model.all
end
def create(attributes)
scoped_model.create!(attributes)
end
private
def check_record_matches(record)
raise(ArgumentError, "record model doesn't match the model of the repository") if not record.class == self.model
end
def scoped_model
if #scope
#scope.send(#association_name)
else
self.model
end
end
end
And then you could for example have a Post repository.
class PostRepository < GenericRepository
set_model Post
# override all because we also want to fetch the comments in 1 go.
def all
scoped_model.all(:include => :comments)
end
def count()
scoped_model.count
end
end
Just instantiate it in your controller in a before_filter or initialize or wherever. In this case I'm scoping it to the current_user so that it only fetches those records and automatically create posts only for the current user.
def initialize
#post_repository = PostRepository.new(:scope => #current_user, :association_name => 'posts')
end
def index
#posts = #post_repository.all
respond_with #posts, :status => :ok
end
I came across https://github.com/bkeepers/morphine which is a tiny DI framework. It could work for you :) But DI isn't a heavily used pattern in ruby. Also, I instantiate my repos in order to scope them to a current user or something else.
I'm on a quest to find the right way to do just what you ask and do a little write-up about it if I ever do find it. But for now it's already sufficient to make the clean cut between persistance & my controllers. If this is done properly it won't be a big hassle to switch to a different system later on. Or add caching etc.
Well, ActiveRecord already provides abstract persistence layer - it has several different adapters allowing it to use different database backends. Also, it's open-source so you are free to take a look at how it has been achieved.
Upon the first glance you can see that it also has an AbstractAdapter that all other adapters inherit, however, as Ruby is dynamic, duck-typing language, AbstractAdapter doesn't have to contain abstract methods which will be overridden in children classes, neither defines a "contract" that they should honour.
Edit:
Here's a simple sketch on how you could abstract away your storage in Ruby, not sure which pattern exactly it is:
# say you have an AR model of a person
class Person < ActiveRecord::Base
end
# and in-memory store of persons (simply, a hash)
IN_MEMORY_STORE = {
:Person => ['Tim', 'Tom', 'Tumb']
}
# this will abstract access
class MyAbstractModel
def initialize item, adapter
#item = item
#adapter = adapter
end
# get all elements from the store
def all
case #adapter
when :active_record
# pull from database:
Object.const_get(#item).all
when :in_memory_store
# get from in-memory store
IN_MEMORY_STORE[#item]
else
raise "Unknown adapter"
end
end
end
# get all Persons from in-memory storage...
p MyAbstractModel.new(:Person, :in_memory_store).all
# ...and from a database
p MyAbstractModel.new(:Person, :active_record).all
#serverinfo, I don't know much about C#. But when I came to Ruby from a Java/C background, I was blown away when I realized how flexible this language really is. You say that your real problem here is to "abstract away your persistence layer and make it exchangeable". You also asked "how will I write the business logic".
I suggest that you throw away your preconceptions and ask yourself: "how would I like to express data access/storage within my business logic layer"? Don't worry about what you think can or can't be done; if you can figure out how you would like the interface to work, there is probably a way it can be done in Ruby.
You will also have to decide how you want to specify the concrete implementation to be used. Is it possible you will want to use a different data store for different model objects? Might you want to switch at run-time? Would you like to specify the backend to be used in a configuration file, or in code? If you can decide what you want to do, there are lots of people on Stack Overflow who can help you figure out how to do it.

How to get the current instance module in Ruby

That title doesn't really explain everything so here goes. I have two Rails engines that share some functionality (ie. user model and authentication). I have a base User class and then two other User classes that inherit from this base class for each app like so:
class User; end
class App1::User < ::User; end
class App2::User < ::User; end
My authentication has a method similar to the following
def user_from_session
User.find_by_id(session[:user_id])
end
which is included in my application_controller. My problem here is that when a user is fetched... it always uses the base User class. What I really want is to be able to fetch a User that is the same type as the app calling that method.
For instance, if a user is on SomeController:
class App1::SomeController < ApplicationController; end
I want the method in the application_controller to pull out the App1 so that it instantiates an App1::User rather than just a User
Is this possible?
I'm NOT looking for a solution that involves two user_from_session methods, one for each application. I am aware of how to implement that. I'm more interested in know if this type of thing is possible in Ruby.
Though I'd caution you to find a better, less hacky way to do this, here's how you might do it:
def user_from_session
# App1::Whatever::FooController -> App1::Whatever
module_name = self.class.name.split('::')[0..-2].join('::')
# App1::Whatever -> App1::Whatever::User
user_class = "#{module_name}::User".constantize
# App1::Whatever::User.find_by_id(...)
user_class.find_by_id(session[:user_id])
end

Where to put user access controls? The controller or the model?

I understand that we're supposed to avoid putting logic in the controller. So what is the proper way to implement things like user access controls. Let's suppose I have User, where each instance has a flag method admin? that determines whether the user can access information from other users.
Option 1: Put access controls in custom model
Model:
class User < ActiveRecord::Base
def self.get_list(accessor)
return [] unless accessor.admin?
self.all
end
end
Controller:
class UsersController < ApplicationController
def index
#users = User.get_list(current_user)
end
end
current_user would probably be defined somewhere in the application controller.
Option 2: Put access controls in the controller
Model:
class User < ActiveRecord::Base
end
Controller:
class UsersController < ApplicationController
def index
#users = current_user.admin? User.all : []
end
end
There are also some peripheral consequences such as where tests go and how they're implemented.
My instinct is that the first of the two options is preferable, but I've only ever used option 2 in the past. Also, it seems like the generally accepted (as far as I can tell) practice of putting on action-wide access filters is done at the controller level as in:
class UsersController < ApplicationController
before_filter :verify_logged_in
end
Any logic controlling routing of your application belongs in your controller. As for your example, the first is preferable but really there's not much in it.
It's easy for opinionated frameworks make us almost obsessive about doing things in a perceived correct way. In your example such a tiny amount of logic would, in my opinion, be perfectly fine to leave in your controller. If you were to abstract it, give it a descriptive name that described better what the method is doing otherwise you're simply making your code needlessly difficult to read.
As a rails rookie, the second option to me seems far easier to read and comphrehend. I prefer how I can read the single line in the controller and see exactly what you are doing.
In the first example, this logic is hidden someplace else (obviously the model, but I'm a rookie remember!) and seems slightly verbose (for this particular example).
I don't mean to suggest keeping it easier for new kids is A Good Thing, just pointing out a preference.

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.

Determine the domain in an ActiveRecord model

I am in the middle of migrating my application from using subdirectories for userspace to subdomains (ie. domain.com/~user to user.domain.com). I've got a method in my user class currently to get the "home" URL for each user:
class User
def home_url
"~#{self.username}"
# How I'd like to do it for subdomains:
#"http://#{self.username}.#{SubdomainFu.host_without_subdomain(request.host)}"
end
end
I'd like to update this for subdomains, but without hardcoding the domain into the method. As you can see, I am using the subdomain-fu plugin, which provides some methods that I could use to do this, except that they need access to request, which is not available to the model.
I know it's considered bad form to make request available in a model, so I'd like to avoid doing that, but I'm not sure if there's a good way to do this. I could pass the domain along every time the model is initialized, I guess, but I don't think this is a good solution, because I'd have to remember to do so every time a class is initialized, which happens often.
The model shouldn't know about the request, you're right. I would do something like this:
# app/models/user.rb
class User
def home_url(domain)
"http://#{username}.#{domain}"
end
end
# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
# ...
def domain
SubdomainFu.host_without_subdomain(request.host)
end
# Make domain available to all views too
helper_method :domain
end
# where you need it (controller or view)
user.home_url(domain)
If there is such a thing as a canonical user home URL, I would make a configurable default domain (e.g. YourApp.domain) that you can use if you call User#home_url without arguments. This allows you to construct a home URL in places where, conceptually, the "current domain" does not exist.
While molf's answer is good, it did not solve my specific problem as there were some instances where other models needed to call User#home_url, and so there would be a lot of methods I'd have to update in order to pass along the domain.
Instead, I took inspiration from his last paragraph and added a base_domain variable to my app's config class, which is the set in a before_filter in ApplicationController:
module App
class << self
attr_accessor :base_domain
end
end
class ApplicationController < ActionController::Base
before_filter :set_base_domain
def set_base_domain
App.base_domain = SubdomainFu.host_without_subdomain(request.host)
end
end
And thus, when I need to get the domain in a model, I can just use App.base_domain.

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