I'm using Rails 4. I have a class, Cart, which needs to be accessed within my application.
I want it accessed using the factory pattern:
class CartFactory
def self.obtain_cart_for_user(user)
...
end
end
I need this approach because sometimes, I want to return an existing cart and sometimes create a new one (based upon the age of the cart, its contents, whether the products in it are still available etc).
This is easy enough.
However, I also want to make sure some other future programmer doesn't instantiate a cart directly, or fetch one by any other means, including via model associations, such as:
Cart.new(...)
user.carts.new(...)
Cart.find(id)
Cart.find_by_attribute(blah: blah)
Cart.where(...).first
Is there any way to prevent that?
Well, it's possible to make the constructor private:
private_class_method :new
And of course, you can try making the ActiveRecord query methods (.find, .where etc.) private as well. But to me that sounds like a good way to end up with erratic behaviour. If you were to go this route, make sure your app is thoroughly tested first.
Another route would be for Cart not to extend ActiveRecord::Base (which I'm assuming it does), and instead include only the parts you need, like ActiveRecord::Persistence. If you are willing to dive in deep, check out the parts that are included in the source for ActiveRecord::Base.
Edit: Still one option would be to make Cart itself private within a module that only exposes CartFactory. There's no built-in syntax for a "private class", but it's possible to achieve since Ruby classes are just regular objects. Again, no idea how well ActiveRecord would deal with that.
But lastly there is of course the question of whether you want to do this at all. In general, Ruby is not very good at protecting you from yourself. :) As expressed in the latter linked answer, documentation and trust go a long way.
Related
TL;DR: I don't know how organise my logic domain classes.
I have the model "Application", this model is in the "core" of the App and is the way I "enter" and operate over other models like:
#application = Application.find(params[:application_id])
#application.payment.update_attribute 'active', true
or
unless #application.report.status
or
#application.set_income(params[:income][:new_income])
so the models Payment, Income and Report are basically empty because I initialise the Application model and from there I do things "on cascade" to change the "subordinated" models. But now the Application model has more than forty methods and 600 lines.
I'm doing it right? For instance when I want to add a new Payment I like to do :
payment = Payment.create params
inside the Application model because ActiveRecord "knows" how to handle the foreign keys automatically. I could create the payment inside the Payment model using:
application = Application.find(application_id)
params[:application_id] = application.id
self.create params
but this way, I need to set the Application.id manually and that looks more verbose and not elegant.
So --if I want to reduce my Application model--, should I create modules in APP/lib directory or should I move methods to the other models?
should I create modules in APP/lib directory
Basically, yes, that's what you should do. Although I'd probably make them classes rather than modules. The pattern it sounds like you're after is called "service Objects" (or sometimes "use cases"). What this does is takes the logic from a specific operation you want to perform, and puts it in it's own self-contained class. That class then collaborates with whatever models it needs to. So, your models stay quite small, and your "Service Classes" follow the Single Responsibility Principle. Your controllers then usually call a single "service class" to do what they need to do - so your controllers stay pretty minimal too.
If you google "rails service objects" or similar, you'll find lots of great stuff, but here's some resources to get you started.
Service objects rails casts: https://www.youtube.com/watch?v=uIp6N89PH-c
https://webuild.envato.com/blog/a-case-for-use-cases/
https://blog.engineyard.com/2014/keeping-your-rails-controllers-dry-with-services
http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/ (there's one section on service objects there)
Keep in mind, once you do start using service objects, you don't necessarily have to ALWAYS go through your Application model to get to the related ones. A service object might take an application_id and then do eg. #payment = Payment.find_by(application_id: application_id) and so you don't have to fetch the application instance at all and can manipulate the #payment variable directly.
The fact that Rails makes it "easy" and "pretty" to get to related models doesn't necessarily mean you should do it.
I would not worry about long controller and spec files in Rails.
These files tend to get very long and the usual advice of keeping classes and methods short does not necessarily apply for controllers and their specs.
For example, in our production system user_controller.rb is 8500 lines long and the corresponding user_controller_spec.rb is 7000 lines long.
This is the length of our top 10 controllers
1285 app/controllers/*********_controller.rb
1430 app/controllers/***********_controller.rb
1444 app/controllers/****_controller.rb
1950 app/controllers/****_controller.rb
1994 app/controllers/********_controller.rb
2530 app/controllers/***********_controller.rb
2697 app/controllers/*********_controller.rb
2998 app/controllers/*****_controller.rb
3134 app/controllers/application_controller.rb
8737 app/controllers/users_controller.rb
TL;DR: If your app has four models that are all tied to tables in your database (ie. leveraging ActiveRecord and inheriting from ActiveModel::Base), the framework is pretty opinionated toward using model classes.
Abstractions of the service class pattern can be useful in some cases, but give yourself a break. One of the advantages of Rails is that its supposed to remove a lot of the barriers to development, among many things, by making organization decisions for you. Leverage your model classes.
Let's see if this starts an epic developer bickering war.
Also, its ok to create interfaces in your models for related model creation:
class Application < ActiveModel::Base
has_one :payment
def create_payment(attrs)
payment.create(attrs)
end
end
And by ok, i mean that the framework will allow this. But remember, you're already inheriting from ActiveModel::Base which defines many instance methods, including create.
I would recommend, esp. if this is a small project and you're just getting your feet wet, to use well-named rails controllers to read and write objects to the database:
class ApplicationPaymentsController < ActionController::Base
def create
application = Application.find(params[:id])
application.create_payment(payment_params)
end
private
def payment_params
params.require(:payment).permit(:x, :y) - whatever your attr names are.
end
end
The sleekness you're looking for in abstracting foreign keys in creating a relational record is taken care of for you with Rails associations:
http://guides.rubyonrails.org/association_basics.html (good starting point)
http://apidock.com/rails/ActiveRecord/Associations/ClassMethods/has_one (more explicit docs)
That will help you slim down models if that is your goal. Just for clarification, this is one of those things that devs are extremely opinionated on, one way or another, but the truth is that there are code smells (which should be addressed) and then there are folks who arbitrary preach file length maxes. The most important thing in all of this is readable code.
A good litmus test for refactoring working code is put it down for a few weeks, come back to it, and if its confusing then put in some time to make it better (hopefully guided by already written test coverage). Otherwise, enjoy what you do, especially if you're working solo.
I'm in the process of updating a website I made almost 2 years ago. It was my first real website and I made some mistakes (some more serious that others).
What apparently is one of my biggest is making database calls from the view.
I'm pretty damn sure there is a better way to do this:
Use Case:
Someone fills out a form for a new subject, populating the Subject table, and they have been marked "enrolled", Subject.enrolled = 1
Based on that, I now need to create a record in 5 other tables (such as Baseline)
Downhill from here, here is my method
Determine if the record exist based on subject_id from Subject (sub)
<$ if Baseline.where(subject_id: sub.subject_id).first != nil $>
If it does not exist, create the record, (otherwise display the link)
<%= Baseline.create(subject_id: sub.subject_id) %>
This all happens in the view, and creates a front-end table with links to each record in the process. So I'm creating records based on for-loop logic...
Question:
So I'm looking for direction. I don't want to guess how to do this - I'm pretty sure the model/controller should do this - I want to learn how to do it correctly. How do I create records automatically, based on a value in a table?
Thank you for your time.
Not quite sure how your domain and code looks like, but to answer this question: 'How do I create records automatically, based on a value in a table?', it seems that you could use ActiveRecord callbacks, like this:
class Subject < ActiveRecord::Base
after_commit :create_baseline_if_enrolled, on: [:create, :update]
private
def create_baseline_if_enrolled
return unless enrolled?
# enrolled? == true, you may create these models here
end
end
To answer your question:
It depends :) This is just one possible solution. Another one would be to put such a custom logic in your SubjectsController and call it directly from the #create, #update methods. Both approaches have pros and cons. For example, abusing callbacks (anywhere) makes code less readable and harder to debug. On the other hand, putting such logic in controllers puts a burden on you that you have to remember about calling it if you happen to be editing subjects in other places (but is more explicit). Whichever way you choose, remember not to make your classes too fat, for example try to use service object pattern to separate such custom logic as soon as you feel like it is getting out of hand. :) And don't forget about tests - when things go wrong, tests make refactoring easier.
I'm working on an app at work. Basic stuff, user signs up (with an associated organization).
Initially I started off with a simple controller -
# Need to check if organization exists already; deny user creation if it does
if #organization.save
#user.save
redirect_to user_dashboard_path...
I soon found myself in a callback soup:
After the organization is validated, we save the user.
When the organization is created, I create another two models, EmailTemplate and PassTemplate (an organization has_one :email_template, has_one :pass_template)
after_create :init_company, :init_email_template, :init_pass_template, :init_form
Each of those callbacks generally calls method on the model, something like:
def init_email_template
self.email_template.create_with_defaults
end
Initially I thought this was quite clever - doing so much behind the scenes, but I've been reading Code Complete by Steve McConnell, and feel this is not simple at all. If I didn't know what was happening already, There's no hint that any time an organization is created it creates 3 associated objects (and some of those objects in turn initialize children objects).
It seems like a bad programming practice, as it obfuscates what's going on.
I thought about moving all of those initalizations to the controller, as an organization is only ever created once:
class OrganizationsController < AC
...
def create
if #organization.save
#organization.create_user
#organization.create_email_template
#organization.create_pass_template
end
That seems like cleaner code, and much easier to follow.
Question 1
*Are there better solutions, or best practices for handling creating associated objects upon creation of the hub object that I'm unaware of?*
Side note - I would have to rewrite a bunch of tests that assume that associations are automatically created via callbacks - I'm okay with that if it's better, easier to understand code.
Question 2
**What about a similar situation with after_save callbacks?**
I have a customer model that checks to see if it has an associated user_account after creation, and if not, creates it. It also creates a Tag model for that user_account once we've created the user_account
class Customer < AR
after_create :find_or_create_user_account
def find_or_create_user_account
if !self.user_account_exists?
#create the user
end
Tag.create(:user_id => self.user_account.id)
end
end
Somewhat simplified, but again, I believe it's not particularly good programming. For one, I'm putting logic to create two different models in a third model. Seems sloppy and again the principle of separating logic. Secondly, the method name does not fully describe what it's doing. Perhaps find_or_create_user_account_and_tag would be a better name, but it also goes against the principle of having the method do one thing- keeping it simple.
After reading about observers and services, my world was thrown for a bit of a loop.
A few months ago I put everything in controllers. It was impossible to test well (which was fine because I didn't test). Now I have skinny controllers, but my models are obese and, I think, unhealthy (not clear, not obvious, harder to read and decipher for another programmer/myself in a few months).
Overall I'm just wondering if there are some good guides, information, or best practices on separation of logic, avoiding callback soup, and where to different sorts of code
Why not the following?
after_create :init_associated_objects
def init_associated_objects
init_company
init_email_template
init_pass_template
init_form
end
My interpretation with "a method should do one thing" isn't strict and that I usually have a method that calls other method (much like the one above). At the end of the day, it's a divide and conquer strategy.
Sometimes I create utility POROs (plain old ruby objects) when it doesn't make sense to have an AR model but a group of functionalities is a class' responsibility. Reports, for instance, are not AR-backed models but it's easier when a report that needs to call multiple models is just instantiated once where the reporting period start and end are instance variables.
A rule of thumb that I follow: if I instantiate the models outside of the whole MVC stack (e.g. Rails console), the things that I expect to happen should stay inside the model.
I don't claim best practices but these have worked for me so far. I'm sure other people would have a better idea on this.
I know the dogma says to not access current_user in a model but I don't fully agree with it. For example, I want to write a set of logging functions when an action happens via a rails callback. Or simply writing who wrote a change when an object can have multiple people write to it (not like a message which has a single owner). In many ways, I see current_user more as config for an application - in other words make this app respond to this user. I would rather have my logging via the model DSL rather than in the action where it seems REALLY out of place. What am I missing?
This idea seems rather inelegant Access current_user in model
as does this: http://rails-bestpractices.com/posts/47-fetch-current-user-in-models
thx
edit #1
So my question isn't if there are gems that can do auditing / logging. I currently use paper_trail (although moving away from it because I can do same functionality in approx 10 lines of ruby code); it is more about whether current_user should never be accessed in the model - I essentially want to REDUCE my controller code and push down logic to models where it should be. Part of this might be due to the history of ActiveRecord which is essentially a wrapper around database tables for which RoR has added a lot of functionality over the years.
You've given several examples that you'd like to accomplish, I'll go through the solution to each one separately:
I want to write a set of logging functions when an action happens via
a rails callback
Depending on how you want to log (DB vs writing to the logger). If you want to log to the DB, you should have a separate logging model which is given the appropriate information from the controller, or simply with a belongs_to :user type setup. If you want to write to the logger, you should create a method in your application controller which you can call from your create and update methods (or whatever other actions you wanted to have a callback on.)
Or simply writing who wrote a change when an object can have multiple people write to it
class Foo < ActiveRecord::Base
belongs_to :user, as: :edited_by
end
class FooController < ApplicationController
def update
#foo = Foo.find(params[:id])
#foo.attributes = params[:foo]
#foo.edited_by = current_user
end
end
I think you're misunderstanding what the model in Rails does. Its scope is the database. The reason it can't access current_user, is because the current user is not stored in the database, it is a session variable. This has absolutely nothing to do with the model, as this is something that can not exist without a browser.
ActiveRecord::Base is not a class that is designed to work with the browser, it is something that works with the database and only the database. You are using the browser as an interface to that model, but that layer is what needs to access browser specific things such as session variables, as your model is extending a class that is literally incapable of doing so.
This is not a dogma or style choice. This is a fact of the limitations of the class your model is extending from. That means your options basically boil down to extending from something else, handling it in your controller layer, or passing it to the model from your controller layer. ActiveRecord will not do what you want in this case.
The two links you show (each showing imho the same approach) is very similar to a approach I still use. I store the current_user somewhere (indeed thread-context is the safest), and in an observer I can then create a kind of audit-log of all changes to the watched models, and still log the user.
This is imho a really clean approach.
An alternative method, which is more explicit, less clean but more MVC, is that you let the controller create the audit-log, effectively logging the actions of the users, and less the effects on different models. This might also be useful, and in one website we did both. In a controller you know the current-user, and you know the action, but it is more verbose.
I believe your concerns are that somehow this proposed solution is not good enough, or not MVC enough, or ... what?
Another related question: How to create a full Audit log in Rails for every table?
Also check out the audited gem, which solves this problem as well very cleanly.
Hope this helps.
I have a simple model called Party with a corresponding table called parties. There's also a controller with all the usual CRUD actions and so on. This model is used in a website and only one admin user is allowed to edit the parties - everyone else is allowed to call GET actions (index, show). Nothing special so far.
Now I need to do the following: The admin would like to choose a single Party at a time for special presentation (the selected Party is showing up on the start page of the application). The most important thing is, that there's only ONE party at time selected.
How would you solve this problem? Boolean Flag in Party model? Save the selection (id of the party) somewhere outside the database? Implement a new model with a has_one relation to Party (seems like overkill to me)?
I hope my explanation is good enough to understand the issue.
A simple "front_page" attribute would suffice or another model like you mentioned, using the has_one relationship would be fine as well.
Using another model would allow you to maintain some more information, like how long should it remain on the front page (expiration date?) or how many times it was featured (assuming a party can be featured twice). It really depends on other requirements for your system.
You also might be able to get away with a simple implementation of the Singleton pattern as well. There's a quick description on the Rails Wiki of making an ActiveRecord object a Singleton (see below): http://wiki.rubyonrails.org/rails/pages/TipsAndTricks
Making a singleton ActiveRecord object
If you have a table with just one
entry, useful for keeping track of a
number sequence for databases without
sequences, you can use the singleton
module included with ruby like so:
require 'singleton'
class Master < ActiveRecord::Base
include Singleton
def initialize(args=nil) super(args) if record = Master.find(:first)
self.attributes = record.attributes end end def next_tracking_number increment!
(:current_tracking_number) current_tracking_number end def
self.next_tracking_number instance.next_tracking_number
end
end
Update:
This is a very poor code example (was copied and pasted from the Rails Wiki, which had no formatting). I would highly recommend the [Ruby Design Patterns] book which tackles many of the GoF design patterns in greater detail (while making them applicable to Ruby applications). But Google should return you some good resources for using the Singleton pattern in Ruby.2
I would go for the boolean flag and create nested singleton resource (promoted), which I would implement in PartiesController itself (set_promoted_party and get_promoted_party actions). For these I would create two new routes:
PUT /parties/promoted/:party_id # to set the promoted party
GET /parties/promoted/:party_id # to get the promoted_party
I would add a second model that had a has_one relationship in order to keep the app RESTful and simple. Also, this way, you can keep a history of special Parties, and track other meaningful information related to the special parties.
Personally I'm very strong on data integrity being enforced by my database so would probably add that extra table and enforce it as a foreign key constraint there.
It can seem like overkill, but is the only* solution that prevents data integrity issues.
Could you maybe add it as a field to the admin table/model - which would be an enforced foreign key to the party table?
*Another solution would be a database trigger that checks no other rows are the selected party but I tend to shy away from such solutions.
Keep it simple. Put a promoted_party.yml file in your config directory that the controllers write to and read from. The contents can be as simple as this:
---
party_id: 123
Done. If you need more integrity or fancier relationships later, implement that later, not now.
For deployments, just make sure the file is symlinked to a shared directory to survive application upgrades.