Quite new to Rails and have run into an issue I just can't seem to figure out.
I have 2 models, User & Post. Users will have a "name" attribute, Posts will have a "title" attribute.
In both cases, I would like to also maintain a slug that will, on before_save, convert the appropriate column to a "sluggified" version and store that as the slug. I've already got the logic I want in place and have had this working, however, I'd like to abstract the behavior into a Concern.
I cannot seem to figure out a way to set this up - mostly because of the dynamic nature of the source field. I'd like to be able to do something like the following:
class User < ActiveRecord::Base
include Sluggable
act_as_slug :name
end
class Post < ActiveRecord::Base
include Sluggable
act_as_slug :title
end
Unfortunately, no matter what I've tried on the implementation of the concern, I've run into walls.
While I'd like to know what type of implementation is possible either way, I'd also be interested in hearing if this is a good use case for concerns or not?
This seems to work, in the event anyone else is looking for an answer (definitely open to better suggestions from those with more experience). The models look as suggested in the original post.
module Sluggable
extend ActiveSupport::Concern
included do
before_save :generate_slug
class_attribute :sluggable_attribute
def generate_slug
self.sluggify(self.class.sluggable_attribute)
end
def sluggify(attribute)
# Sluggify logic goes here
end
end
module ClassMethods
def acts_as_slug(value)
self.sluggable_attribute = value
end
end
end
Related
I've got a Rails application that is multi-tenant. Every model has an account_id, belongs to an account, and has a default scope to a current account id:
class Derp < ApplicationRecord
default_scope { where(account_id: Account.current_id) }
belongs_to :account
end
This works well and I've used this pattern in production in other apps (I understand that default scopes are frowned upon, but this is an accepted pattern. See: https://leanpub.com/multi-tenancy-rails).
Now here's the kicker - I have one client (and potentially more down the line, who knows), who wants to run the software on their own server. To solve this, I simply made a Server model with a type attribute:
class Server < ApplicationRecord
enum server_type: { multitenant: 0, standalone: 1 }
end
Now on my multi-tenant server instance, I simply make one Server record and set the server_type to 0, and on my standalone instance I set it to 1. Then I've got some helper methods in my application controller to help with this, namely:
class ApplicationController < ActionController::Base
around_action :scope_current_account
...
def server
#server ||= Server.first
end
def current_account
if server.standalone?
#current_account ||= Account.first
elsif server.first.multitenant?
#current_account ||= Account.find_by_subdomain(subdomain) if subdomain
end
end
def scope_current_account
Account.current_id = current_account.id
yield
rescue ActiveRecord::RecordNotFound
redirect_to not_found_path
ensure
Account.current_id = nil
end
end
This works, but I've got large record sets that I'm querying on this particular standalone client (70,000 records). I've got an index on the account_id, but it took my main customers table from 100ms to 400ms on my development machine.
Then I realized: standalone servers really don't need to concern themselves with the account id at all, especially if it is going to affect performance.
So really all I've got to do is make this line conditional:
default_scope { where(account_id: Account.current_id) }
I'd like to do something like this:
class Derp < ApplicationRecord
if Server.first.multitenant?
default_scope { where(account_id: Account.current_id) }
end
end
But obviously that syntax wrong. I've seen some other examples on Stack Overflow for conditional scopes, but none seem to work with a conditional statement based on a completely separate model. Is there a way to accomplish something like that in Ruby?
EDIT: Kicker here that I just realized is that this will only solve the speed issue for the one standalone server, and all the multi-tenant accounts will still have to deal with querying with the account_id. Maybe I should focus on that instead...
I would avoid using default_scope as I've been bitten by it in the past. In particular, I've had places in an application where I want to definitely have it scoped, and other places where I don't. The places where I want the scoping typically end up being controllers / background jobs and the places where I don't want / need it end up being the tests.
So with that in mind, I would opt for an explicit method in the controller, rather than an implicit scoping in the model:
Whereas you have:
class Derp < ApplicationRecord
if Server.first.multitenant?
default_scope { where(account_id: Account.current_id) }
end
end
I would have a method in the controller called something like account_derps:
def account_derps
Derp.for_account(current_account)
end
Then wherever I wanted to load just the derps for the given account I would use account_derps. I would then be free to use Derp to do an unscoped find if I ever needed to do that.
Best part about this method is you could chuck your Server.first.multitenant? logic here too.
You mention another problem here:
This works, but I've got large record sets that I'm querying on this particular standalone client (70,000 records). I've got an index on the account_id, but it took my main customers table from 100ms to 400ms on my development machine.
I think this is most likely due to a missing index. But I don't see the table schema here or the query so I don't know for certain. It could be that you're doing a where query on account_id and some other field, but you've only added the index to the account_id. If you're using PostgreSQL, then an EXPLAIN ANALYZE before the query will point you in the right direction. If you're not sure how to decipher its results (and sometimes they can be tricky to) then I would recommend using the wonderful pev (Postgres EXPLAIN Visualizer) which will point you at the slowest parts of your query in a graphical format.
Lastly, thanks for taking the time to read my book and to ask such a detailed question about a related topic on SO :)
Here's my solution:
First, abstract the account scoping stuff that any account scoped model will have to an abstract base class that inherits from ApplicationRecord:
class AccountScopedRecord < ApplicationRecord
self.abstract_class = true
default_scope { where(account_id: Account.current_id) }
belongs_to :account
end
Now any model can cleanly be account scoped like:
class Job < AccountScopedRecord
...
end
To solve the conditional, abstract that one step further into an ActiveRecord concern:
module AccountScoped
extend ActiveSupport::Concern
included do
default_scope { where(account_id: Account.current_id) }
belongs_to :account
end
end
Then the AccountScopedRecord can do:
class AccountScopedRecord < ApplicationRecord
self.abstract_class = true
if Server.first.multitenant?
send(:include, AccountScoped)
end
end
Now standalone accounts can ignore any account related stuff:
# Don't need this callback on standalone anymore
around_action :scope_current_account, if: multitenant?
# Method gets simplified
def current_account
#current_account ||= Account.find_by_subdomain(subdomain) if subdomain
end
The Stage
Lets talk about the most common type of association we encounter.
I have a User which :has_many Post(s)
class User < ActiveRecord::Base
has_many :posts
end
class Post < ActiveRecord::Base
belongs_to :user
end
Problem Statement
I want to do some (very light and quick) processing on all the posts of a user. I am looking for the best way to structure my code to achieve it. Below are a couple of ways and why they work or don't work.
Method 1
Do it in the User class itself.
class User < ActiveRecord::Base
has_many :posts
def process_posts
posts.each do |post|
# code of whatever 'process' does to posts of this user
end
end
end
Post class remains the same:
class Post < ActiveRecord::Base
belongs_to :user
end
The method is called as:
User.find(1).process_posts
Why doesn't this look the best way to do it
The logic of doing something with the posts of the user should really belong to the Post class. In a real world scenario, a user might also have :has_many relations with a lot of other classes e.g. orders, comments, children etc.
If we start adding similar process_orders, process_comments, process_children (yikes) methods to the User class, it'll result in one giant file with lots of code much of which could (and should) be distributed to where it belongs i.e. the target associations.
Method 2
Proxy Associations and Scopes
Both of these constructs require addition of methods/code to the User class which again makes it bloated. I'd rather have all implementation shifted to the target classes.
Method 3
Class Method on target Class
Create class methods in the target class and call those methods on the User object.
class User < ActiveRecord::Base
has_many :comments
# all target specific code in target classes
end
class Post < ActiveRecord::Base
belongs_to :user
# Class method
def self.process
Post.all.each do |post| # see Note 2 below
# code of whatever 'process' does to posts of this user
end
end
end
The method is called as:
User.find(1).posts.process # See Note 1 below
Now, this looks and feels better than Method 1 and 2 because:
User model remains clutter free.
The process function is called process instead of process_posts. Now we can have a process for other classes as well and invoke them as: User.find(1).orders.process etc. instead of User.find(1).process_orders (Method 1).
Note 1:
Yes you can call a class method like this on a association. Read why here. TL;DR is that User.find(1).posts returns a CollectionProxy object which has access to class methods of the target (Post) class. It also conveniently passes a scope_attributes which stores the user_id of the user which called posts.process. This comes handy. See Note 2 below.
Note 2:
For people not sure whats going on when we do a Post.all.each in the class method, it returns all the posts of the user this method was called on as against all the posts in the database.
So when called as User.find(99).posts.process, Post.all executes:
SELECT "notes".* FROM "posts" WHERE "posts"."user_id" = $1 [["user_id", 99]]
which are all the posts for User ID: 99.
Per #Jesuspc's comment below, Post.all.each can be succinctly written as all.each. Its more idiomatic and doesn't make it look like we are querying all posts in the database.
The Answer I am looking for
Explains what is the best way to handle such associations. How do people do it normally? and if there are any obvious design flaws in Method 3.
There's a fourth option. Move this logic out of the model entirely:
class PostProcessor
def initialize(posts)
#posts = posts
end
def process
#posts.each do |post|
# ...
end
end
end
PostProcessor.new(User.find(1).posts).process
This is sometimes called the Service Object pattern. A very nice bonus of this approach is that it makes writing tests for this logic really simple. Here's a great blog post on this and other ways to refactor "fat" models: http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/
Personally, I think that Method 1 is the cleanest one. It will be very clean and understandable write something like this:
Class User < ActiveRecord::Base
has_many :posts
def process_posts
posts.each do |post|
post.process
end
end
end
And put all the logic of process method in Post model (with an instance variable):
Class Post < ActiveRecord::Base
belongs_to :user
def process
# Logic of your Post process
end
end
That way, the very logic of a Post process belong to Post class. Even if your User model will have many "process" functions, these will be very basic and small. That seems very clean to me, as a developer.
Method 3 has many technical implications that are pretty complex and unintuitive (yourself had to clarify your question).
NOTE: If you want better performance, maybe you should use eager loading to reduce ActiveRecord calls, but that is out of the scope of this question.
First of all excuse me for the opinionated answer.
ActiveRecord models are a controversial matter. Its essence is against the Single responsibility principle since they handle both database interaction via class methods and domain objects (which use to implement their own behaviour) via its instances. At the same time they also break the Liskov Substitution Principle because the models are not sub cases of ActiveRecord::Base and implement their own set of methods. And finally the ActiveRecord paradigm often leads to code that breaks the Law of Demeter, as in your proposal for the third method:
User.find(1).posts.process
Thus, there is a trend that in order to reduce coupling would recommend to use ActiveRecord objects only to interact with the database and therefore no behaviour should be added to them (in your case the process method). Under my point of view that is the lesser evil, even though it is still not a perfect solution.
So if I were to implement what you describe I would have a ProcessablePostsCollection object (where the name Processable can be customised to better describe what the processing is about, or even neglected completely so you would simple have a PostsCollection class) that would probably be a wrapper over a list of posts using SimpleDelegator and would have a method process.
class ProcessablePostsCollection < SimpleDelegator
def self.from_collection(collection)
new collection
end
def initialize(source)
super source
end
def process
# code of whatever 'process' does to posts
end
end
And the usage would be something like:
ProcessablePostsCollection.from_collection(User.find(1).posts).process
even though the from_collection and the call to process should happen in different clases.
Also, in case you have a big posts table it would probably be wise to process stuff in batches. For that your process method could call find_in_batches on your posts ActiveRecord::Relation.
But as always it depends on your needs. If you are simply building a prototype is perfectly fine to let your models grow fat, and if you are building an enormous application Rails itself is probably not going to be the best choice since discourages some OOP best practises with things such as ActiveRecord models.
You shouldn't be putting this in the User model - put it in Post (unless - of course - the scope of process involves the User model directly) :
#app/models/post.rb
class Post < ActiveRecord::Base
def process
return false if post.published?
# do something
end
end
Then you can use an ActiveRecord Association Extension to add the functionality to the User model:
#app/models/user.rb
class User < ActiveRecord::Base
has_many :posts do
def process
proxy_association.target.each do |post|
post.process
end
end
end
end
This will allow you to call...
#user = User.find 1
#user.posts.process
I have Customer and each customer has_many Properties. Customers belong to a Company.
I'm trying to add a certain Property to each one of a single Company's Customers. I only want this change to happen once.
I'm thinking about using a migration but it doesn't seem right to create a migration for a change that I only ever want to happen once, and only on one of my users.
Is there a right way to do this?
You can just use rails console.
In rails c:
Company.where(conditions).last.customers.each do |customer|
customer.properties << Property.where(condition)
customer.save!
end
Validation
Depending on how you're changing the Customer model, I'd include a simple vaidation on the before_update callback to see if the attribute is populated or not:
#app/models/Customer.rb
class Customer < ActiveRecord::Base
before_update :is_valid?
private
def is_valid?
return if self.attribute.present?
end
end
This will basically check if the model has the attribute populated. If it does, it means you'll then be able to update it, else it will break
--
Strong_Params
An alternative will be to set the strong_params so that the attribute you want to remain constant will not be changed when you update / create the element:
#app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
...
private
def strong_params
params.require(:model).permit(:only, :attributes, :to, :update)
end
end
It would be much more helpful if you explained the context as to why you need this type of functionality - that will give people the ability to create a real solution, instead of proposing ideas
I'm looking for some best-practice advice for the following situation.
I have the following skeleton ActiveRecord models:
# user.rb
class User < ActiveRecord::Base
has_many :country_entries, dependent: destroy
end
# country_entry.rb
class CountryEntry < ActiveRecord::Base
belongs_to :user
validates :code, presence: true
end
Now suppose I need to get a comma-separated list of CountryEntry codes for a particular user. The question is, where do I put this method? There are two options:
# user.rb
#...
def country_codes
self.country_entries.map(&:code)
end
#...
-or-
# country_entry.rb
#...
def self.codes_for_user(user)
where(user_id: user.id).map(&:code)
end
#...
And so the APIs would be: #current_user.country_codes -or- CountryEntry.codes_for_user(#current_user)
Seems like placing the code in country_entry.rb decouples everything a little more, but it makes the API a little uglier. Any general or personal-experience best practices on this issue?
Instance method VS Class method: If the method is for an instance, of course it is better to be an instance method.
In user model VS in Coutry model: User model wins. Law of Demeter suggests one dot only in Ruby. If you have chance to do that, of course it's better to follow.
Conclusion: Your first method wins.
# user.rb
def country_codes
self.country_entries.map(&:code)
end
Add: Reference for Law of Demeter
http://en.wikipedia.org/wiki/Law_of_Demeter
http://rails-bestpractices.com/posts/15-the-law-of-demeter
http://devblog.avdi.org/2011/07/05/demeter-its-not-just-a-good-idea-its-the-law/
Now this is really an interesting question. And it has so many answers ;-)
From your initial question I would suggest you put the code in the association itself
class User < ActiveRecord::Base
has_many :country_entries do
def codes
proxy_association.owner.country_entries.map(&:code)
end
end
end
so you could do something like this
list_of_codes = a_user.country_entries.codes
Now obviously this is a violation of the Law of Demeter.
So you would best be advised to offer a method on the User object like this
class User < ActiveRecord::Base
has_many :country_entries do
def codes
proxy_association.owner.country_entries.map(&:code)
end
end
def country_codes
self.country_entries.codes
end
end
Obviously nobody in the Rails world cares about the Law of Demeter so take this with a grain of salt.
As for putting the code into the CountryEntry class I am not sure why you would do this. If you can look up country codes only with the user I dont see the need to create a class method. You are anyway only able to look that list up if you have a User at hand.
If however many different objects can have a country_entries association than it makes sense to put it as a class method into CountryEntry.
My favorite would be a combination of LOD and a class method for reuse purposes.
class User < ActiveRecord::Base
has_many :country_entries
def country_codes
CountryEntry.codes_for_user(self)
end
end
class CountryEntry < ActiveRecord::Base
belongs_to :user
validates :code, presence: true
def self.codes_for_user(some_id)
where(ref_id: some_id).map(&:code)
end
end
In terms of API developers get from the two proposals, adding to the user model seems pretty straightforward. Given the problem:
Now suppose I need to get a comma-separated list of CountryEntry codes for a particular user.
The context is made of a user, for which we want to get the code list. The natural "entry point" seems a user object.
Another way to see the problem is in terms of responsibilities (thus linking to #robkuz entry on Demeter's). A CountryEntry instance is responsible for providing its code (and maybe a few other things). A CountryEntry class is basically responsible for providing attributes and methods common to all its instances, and no more (well). Getting the list of comma-separated codes is a specialized usage of CountryEntry instances that only User objects care of apparently. In this case, the responsibility belongs to the current user object. Value in the eye of the beholder...
This is inline with most answers on the thread, although in the solutions so far, you do not get a comma-separated list of codes, but an array of codes.
In terms of performance, note there is probably a difference too because of lazy evaluation. Just a note---someone more deeply familiar with ActiveRecord could comment on that!
I think #current_user.country_codes is a better choice in this case because it will be easier to use in your code.
I have been researching on the best approach for my problem which I originally had implemented as a single table inheritance but am deeply concerned about the scalability, as potentially will have thousands of columns in the table.
So the problem is I would like to have products which the methods of each are exactly the same the only difference being the attributes each one contains. It seems that in this situation that mutli-class inheritance (not supported natively in rails?) would be the best approach or some sort of polymorphic associations.
I want to work towards the following
#product.rb
Class Product < ActiveRecord::Base
attr_accessible :title .....
def to_s # some arbitrary method used by all extending classes
....
end
end
#book.rb
class Book < Product
attr_accessible :author...
end
So I want the book to inherit the methods from product and not for the product to know about the attributes required by each subclass. And if possible get all of the products through one query.
I need to know the best way of approaching this, and if I am doing it completely wrong, please note the code written above is just for example to simplify my problem.
What you can do is create a module and include it in several different models.
First, create a file in your lib directory
i.e.) my_module.rb
module MyModule
def full_name
"#{first_name} #{last_name}"
end
end
Then, make sure the module is loaded when your Rails App starts:
In config/application.rb:
config.autoload_paths += %W(#{config.root}/lib)
Finally, include it in your models:
i.e.) app/models/thing.rb
class Thing < ActiveRecord::Base
attr_accessible :first_name, :last_name
include AdditionMod
end
You can test it in the console:
#thing = Thing.create(first_name: "Awesome", last_name: "Module")
#thing.full_name
=> "Awesome Module"
Found out that I can use H-store in conjunction with postgres that allows me to have a column that contains a schema less hash that can be used with the power of postgres (for an example take a look at http://hstoredemo.herokuapp.com/)