Gunnar Wolf

This is the third plugin I have been working on for Rails - It's the one that still needs most work to be fully usable (for what I originally envisioned it), but is almost there - I have not touched it (nor the other two I recently presented here, acts_as_catalog and Real FK because real-life has demanded my time on various other fronts.
Anyway, this is IMHO the most interesting of the three plugins I've written so far.
So, following what I did with the other plugins: You can go to acts_as_magic_model's main page, or jump straight to its SVN repo. And the basic description follows:
Rails plugin to allow for extensible models, where inter-model relations are inferred from the database's structure, and not necessarily from explicit declarations in the models.
This means, when one of your models acts_as_magic_model, this plugin will try to infer all the basic relations (has_many, belongs_to and has_and_belongs_to_many) its base table has with other tables in the database, adapting the model correspondingly.

Using the plugin

In order to use this plugin, you only have to declare it in your model. As an example, say you have the proverbial project-management system, where you have projects (each of which can be of several different types) and people, and a HABTM relation between people and projects. So, you have the following tables (expressed as migrations here):

    create_table :people, :force => true do |t|
      t.column :name, :string
    end
 
    create_table :project_types, :force => true do |t|
      t.column :name, :string
    end
 
    create_table :projects, :force => true do |t|
      t.column :name, :string
      t.column :project_type_id, :integer
    end
 
    create_table :people_projects, :force => true, :id => false do |t|
      t.column :person_id, :integer
      t.column :project_id, :integer
    end

    class Person < ActiveRecord::Base
      acts_as_magic_model
    end
 
    class Project < ActiveRecord::Base
      acts_as_magic_model
    end
 
    class ProjectType < ActiveRecord::Base
      acts_as_magic_model
    end