Rails model without database

I want to create a Rails (2.1 and 2.2) model with ActiveRecord validations, but without a database table. What is the most widely used approach? I've found some plugins that claim to offer this functionality, but many of them don't appear to be widely used or maintained. What does the community recommend I do? Right now I am leaning toward coming up with my own solution based on this blog post.


I think the blog post you are linking is the best way to go. I would only suggest moving the stubbed out methods into a module not to pollute your code.

There is a better way to do this in Rails 3: http://railscasts.com/episodes/219-active-model

This is an approach I have used in the past:

In app/models/tableless.rb

class Tableless < ActiveRecord::Base
  def self.columns
    @columns ||= [];

  def self.column(name, sql_type = nil, default = nil, null = true)
    columns << ActiveRecord::ConnectionAdapters::Column.new(name.to_s, default,
      sql_type.to_s, null)

  # Override the save method to prevent exceptions.
  def save(validate = true)
    validate ? valid? : true

In app/models/foo.rb

class Foo < Tableless
  column :bar, :string  
  validates_presence_of :bar

In script/console

Loading development environment (Rails 2.2.2)
>> foo = Foo.new
=> #<Foo bar: nil>
>> foo.valid?
=> false
>> foo.errors
=> #<ActiveRecord::Errors:0x235b270 @errors={"bar"=>["can't be blank"]}, @base=#<Foo bar: nil>>

just create a new file ending in ".rb" following the conventions you're used to (singular for file name and class name, underscored for file name, camel case for class name) on your "models/" directory. The key here is to not inherit your model from ActiveRecord (because it is AR that gives you the database functionality). e.g.: for a new model for cars, create a file called "car.rb" in your models/ directory and inside your model:

class Car
    # here goes all your model's stuff

edit: btw, if you want attributes on your class, you can use here everything you use on ruby, just add a couple lines using "attr_accessor":

class Car
    attr_accessor :wheels # this will create for you the reader and writer for this attribute
    attr_accessor :doors # ya, this will do the same

    # here goes all your model's stuff

edit #2: after reading Mike's comment, I'd tell you to go his way if you want all of the ActiveRecord's functionality but no table on the database. If you just want an ordinary Ruby class, maybe you'll find this solution better ;)

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