Ruby on Rails 3 (3.1) ActiveModel Associations (tableless nested models)

Question

How to impliment ActiveModel associations (tableless nested models)?

For example:

book has many chapters

With ActiveRecord I would create two models and assosiate them with has_many and belongs_to. But ActiveModel doesn't have such functionality. How can I implement this?

Ninette

Answer 1

You simply can't do it that way. It is not active record.

You can check ActiveModel documentation (and source code) at :

https://github.com/rails/rails/tree/master/activemodel

I guess you have to do it old fashion way, using an array of chapters and a reference to the book in the chapters.

Hope this helps!

Cryptogram

Thank you for your response, Dominic. I'm new to Ruby language, can you explain what you mean by saying "a reference to the book in the chapters"? – Ninette

Happy I helped! So : Your "chapter" class should have a "book" member which you would affect to the actual "book" that the "chapter" is in. In the "book" class, add an array of all the "chapters" that the book contains. – Cryptogram

Answer 2

With rails versions >= 2.3.x you can use the activerecord-tableless gem. With that gem you can have associations and validations without a database.

Update

I have been added as author to the gem and I have updated the gem to support newer Rails versions. So now we can have tableless models with associations in Rails versions >= 2.3

Cheliform

@Tilo you probably already figured out but... You can use ActiveModel::Model api.rubyonrails.org/classes/ActiveModel/Model.html – Leastwise

Answer 3

You can check out this answer for another way to do it.

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

    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)
    end 

    attr_accessor :id, :name, :value

    has_many :stuff_things
    has_many :things, :through => :stuff_things

end

Eliathan