I'm building an API wrapper that will query objects from a third-party API and build them into objects to be used in my Rails environment. To do that, I'm building a set of models that use ActiveRecord (for some of its functionality) but are not database backed. I would like to be able to make a call like this:
obj = MyModel.find(1)
And have the code be something like this:
def MyModel.find id
# check for object in cache
# check for object in db
# grab object from API
# return object
end
Am I going to do something horribly wrong if I override the default find method? Am I approaching this in totally the wrong way?
If you are not using a database, then you do not need ActiveRecord. The entire purpose of ActiveRecord is to give you a mapping to a relational database.
I think what you want is for a class to implement certain pieces of what ActiveRecord provides, and Rails 3 has made those pieces into classes that you can include into regular 'ol classes on an as-needed basis. Look at this article for more details: http://www.rubyinside.com/rails-3-0s-activemodel-how-to-give-ruby-classes-some-activerecord-magic-2937.html
For instance, if you only want validations on a class, you can use include ActiveModel::Validations and then you'll get all of the nice error handling and .valid? and validates presence: true kind of behavior you're used to.
I would also suggest the railscast by Ryan Bates: http://railscasts.com/episodes/219-active-model which goes into more detail.
I'm trying to use Models in my Rails application that retrieve information from an external API. What I would like to do is access my data models (which may consist of information resulting from multiple API calls) in a way similar to what an ActiveRecord model would provide (specifically associations, and the same style of chain-able query methods).
My initial instinct was to recreate the parts of ActiveRecord that I wanted and incorporate this API. Not wanting to 'reinvent the wheel' and seeing exactly how much work would be required to add more functionality have made me take a step back and reevaluate how to approach this.
I have found ways to use ActiveRecord without a table (see: Railscast #193 Tableless Model and the blog post here) and looked into ActiveRecord. Because ActiveModel only seems to include Validations I'm not sure that's very helpful in this situation. The workaround to using ActiveRecord without a table seems like the best option, but I suspect there's a cleaner way of doing this that I'm just not seeing.
Here is a gist containing some of the code written when I was trying to recreate the ActiveRecord functionality, borrowing heavily from the ActiveRecord source itself.
My question boils down to: I can get the functionality I want (chaining query methods, relations) by either implementing the workaround to ActiveRecord specified above or recreating the functionality myself, but are these really ideal solutions?
Remember that Rails is still just Ruby underneath.
You could represent the external API as instantiated classes within your application.
class Event
def self.find(id)
#...External http call to get some JSON...#
new(json_from_api)
end
def initialize(json)
#...set up your object here...#
end
def attendees
#...external http call to get some JSON and then assemble it
#...into an array of other objects
end
end
So you end up writing local abstractions to create ruby objects from api calls, you can probably also mix in ActiveModel, or Virtus into it, so you can use hash assignment of attributes, and validations for forms etc.
Take a look at an API abstraction I did for the TfL feed for the tube. service_disruption
I have a Rails app with a few model classes (e.g. Category, Subcategory, User, etc.). In order to implement a not-too-trivial filter functionality, I built a hierarchy of filter classes: FilterCategory, FilterSubcategory, etc., that derive from FilterBase. Each of them uses the appropriate "sister" model class (e.g. Category.find :all).
I quickly realized that I can't simply call the "sister" model class without using "require" first. However, I now suspect that using "require" is the main reason for two other problems I posted here and here, which probably mess up the class caching when config.cache_classes=false.
Is there another way for me to call these other models without requiring them?
I tried using the BaseWithoutTable plugin, but when I call the "sister model", I end up getting "Not a valid constant descriptor: nil", which occurs since Rails looks for "FilterCategory::Category" rather than "Category".
Any thoughts of the best way to do that?
I'm using Rails 2.3.8, Ruby 1.8.7.
Thanks,
Amit
I wonder if you want ::Category - getting Category from the top-level namespace rather than scoping it to FilterCategory?
If your models are in the app/models directory, you shouldn't need to explicitly require them - Rails already takes care of that.
I'm working on a project where the data model is :
implemented in a separate gem
does not use ActiveRecord, nor any relational database storage ( actually it relies on couchdb )
makes usage of namespaces
makes intensive usage of class inheritance
To simplify the schema, let's say we have the following root class :
module Marketplace
module Food
class Fruit
…
end
end
end
And a couple of specialized classes :
module Marketplace
module Food
class Peach < Marketplace::Food::Fruit
…
end
class Tomato < Marketplace::Food::Fruit
…
end
end
end
I'd like Rails to display (and manage) all the Fruits whatever is their nature, without modifying the model witch works perfectly out of Rails.
The issue is that ActionView seems to use a certain number of conventions for defining paths and urls that will be based on the real class names.
So if I present an Apple, in a table with show/delete actions, rails will look for a methods named marketplace_food_apple_path and similar which of course don't exist.
Is there a way to indicate the ActionView::Base structure(s) that an Apple is a Fruit ?
I'd expect this 'base cast' to be 'trivial' for a framework based on Ruby but it seems that this simple example of object oriented model does not work with Rails ?
How do you manage 'complex object' data models in rails ?
Or it is simply out of scope of Rails ?
Thanks for any pointers !
http://railstips.org/blog/archives/2009/05/15/include-vs-extend-in-ruby/ <-- probably what you want, unless you're just looking to argue the single inheritance versus multiple inheritance strawman.
OK as I see there are plenty of useful answers ;).
It basically confirms my doubts on Rails which I see more like a sort of VB : easy to learn, nice for small things (shopping or community sites) but very limited.
Rails is completely out of scope when it gets to handling complex business logic and data !
As Rails 3.0 does not seem to be the answer neither (ok we have several ORM's but we're still unable to use inheritance in the model) I switched to Ramaze, a small framework that makes no assumptions on how the data is organized making it suitable for almost any kind of web needs.
If you are facing model constraints with Rails, maybe you should forget about Rails and check Ramaze !
I'm really enjoying Rails (even though I'm generally RESTless), and I enjoy Ruby being very OO. Still, the tendency to make huge ActiveRecord subclasses and huge controllers is quite natural (even if you do use a controller per resource). If you were to create deeper object worlds, where would you put the classes (and modules, I suppose)? I'm asking about views (in the Helpers themselves?), controllers and models.
Lib is okay, and I've found some solutions to get it to reload in a dev environment, but I'd like to know if there's a better way to do this stuff. I'm really just concerned about classes growing too large. Also, what about Engines and how do they fit in?
Because Rails provides structure in terms of MVC, it's natural to end up using only the model, view, and controller containers that are provided for you. The typical idiom for beginners (and even some intermediate programmers) is to cram all logic in the app into the model (database class), controller, or view.
At some point, someone points out the "fat-model, skinny-controller" paradigm, and intermediate developers hastily excise everything from their controllers and throw it into the model, which starts to become a new trash can for application logic.
Skinny controllers are, in fact, a good idea, but the corollary--putting everything in the model, isn't really the best plan.
In Ruby, you have a couple of good options for making things more modular. A fairly popular answer is to just use modules (usually stashed in lib) that hold groups of methods, and then include the modules into the appropriate classes. This helps in cases where you have categories of functionality that you wish to reuse in multiple classes, but where the functionality is still notionally attached to the classes.
Remember, when you include a module into a class, the methods become instance methods of the class, so you still end up with a class containing a ton of methods, they're just organized nicely into multiple files.
This solution can work well in some cases--in other cases, you're going to want to think about using classes in your code that are not models, views or controllers.
A good way to think about it is the "single responsibility principle," which says that a class should be responsible for a single (or small number) of things. Your models are responsible for persisting data from your application to the database. Your controllers are responsible for receiving a request and returning a viable response.
If you have concepts that don't fit neatly into those boxes (persistence, request/response management), you probably want to think about how you would model the idea in question. You can store non-model classes in app/classes, or anywhere else, and add that directory to your load path by doing:
config.load_paths << File.join(Rails.root, "app", "classes")
If you're using passenger or JRuby, you probably also want to add your path to the eager load paths:
config.eager_load_paths << File.join(Rails.root, "app", "classes")
The bottom-line is that once you get to a point in Rails where you find yourself asking this question, it's time to beef up your Ruby chops and start modeling classes that aren't just the MVC classes that Rails gives you by default.
Update: This answer applies to Rails 2.x and higher.
Update: The use of Concerns have been confirmed as the new default in Rails 4.
It really depends on the nature of the module itself.
I usually place controller/model extensions in a /concerns folder within app.
# concerns/authentication.rb
module Authentication
...
end
# controllers/application_controller.rb
class ApplicationController
include Authentication
end
# concerns/configurable.rb
module Configurable
...
end
class Model
include Indexable
end
# controllers/foo_controller.rb
class FooController < ApplicationController
include Indexable
end
# controllers/bar_controller.rb
class BarController < ApplicationController
include Indexable
end
/lib is my preferred choice for general purpose libraries. I always have a project namespace in lib where I put all application-specific libraries.
/lib/myapp.rb
module MyApp
VERSION = ...
end
/lib/myapp/CacheKey.rb
/lib/myapp/somecustomlib.rb
Ruby/Rails core extensions usually take place in config initializers so that libraries are only loaded once on Rails boostrap.
/config/initializer/config.rb
/config/initializer/core_ext/string.rb
/config/initializer/core_ext/array.rb
For reusable code fragments, I often create (micro)plugins so that I can reuse them in other projects.
Helper files usually holds helper methods and sometimes classes when the object is intended to be used by helpers (for instance Form Builders).
This is a really general overview. Please provide more details about specific examples if you want to get more customized suggestions. :)
... the tendency to make huge
ActiveRecord subclasses and huge
controllers is quite natural ...
"huge" is a worrisome word... ;-)
How are your controllers becoming huge? That's something you should look at: ideally, controllers should be thin. Picking a rule-of-thumb out of thin air, I'd suggest that if you regularly have more than, say, 5 or 6 lines of code per controller method (action), then your controllers are probably too fat. Is there duplication that could move into a helper function or a filter? Is there business logic that could be pushed down into the models?
How do your models get to be huge? Should you be looking at ways to reduce the number of responsibilities in each class? Are there any common behaviours you can extract into mixins? Or areas of functionality you can delegate to helper classes?
EDIT: Trying to expand a bit, hopefully not distorting anything too badly...
Helpers: live in app/helpers and are mostly used to make views simpler. They're either controller-specific (also available to all views for that controller) or generally available (module ApplicationHelper in application_helper.rb).
Filters: Say you have the same line of code in several actions (quite often, retrieval of an object using params[:id] or similar). That duplication can be abstracted first to a separate method and then out of the actions entirely by declaring a filter in the class definition, such as before_filter :get_object. See Section 6 in the ActionController Rails Guide Let declarative programming be your friend.
Refactoring models is a bit more of a religious thing. Disciples of Uncle Bob will suggest, for example, that you follow the Five Commandments of SOLID. Joel & Jeff may recommend a more, er, "pragmatic" approach, although they did appear to be a little more reconciled subsequently. Finding one or more methods within a class that operate on a clearly-defined subset of its attributes is one way to try identifying classes that might be refactored out of your ActiveRecord-derived model.
Rails models don't have to be subclasses of ActiveRecord::Base, by the way. Or to put it another way, a model doesn't have to be an analogue of a table, or even related to anything stored at all. Even better, as long as you name your file in app/models according to Rails' conventions (call #underscore on the class name to find out what Rails will look for), Rails will find it without any requires being necessary.
Here's an excellent blog post about refactoring the fat models that seem to arise from the "thin controller" philosphy:
http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/
Basic message is "Don’t Extract Mixins from Fat Models", use service classes instead, the author provides 7 patterns to do so