See magicmodels.rubyforge.org/dr_nic_magic_models for pretty README

Ugly README (from website/index.txt in Textile format): h1. Dr Nic’s Magic Models

If you’ve used Ruby on Rails you’ll have written at least one model class like this:

<pre syntax=‘ruby’> class Person < ActiveRecord::Base

has_many :memberships
has_many :groups, :through => :memberships
belongs_to :family
validates_presence_of :firstname, :lastname, :email

end </pre>

A few minutes later you’ll have wondered to yourself,

<blockquote> Why do I have write my own has_many, belongs_to, and validates_presence_of commands if all the data is in the database schema? </blockquote>

Now, for the very first time, your classes can look like this:

<pre syntax=‘ruby’> class Person < ActiveRecord::Base end </pre>

or, if you are lazy…

<pre syntax=‘ruby’> class Person < ActiveRecord::Base; end </pre>

or, if you read right to the end of this page, this…

<pre syntax=‘ruby’> # Go fish. </pre>

Magic and mystery abound. All for you. Impress your friends, amaze your mother.

NOTE: The gratuitous use of *Dr Nic’s* in the name should only enhance the mystical magikery, for magic needs a magician; and I love magic. I always wanted to create my own magic trick. So I shall be the magician for the sake of magic itself. I look a bit like Harry Potter too, if Harry were 32 and better dressed.

h2. Installation

To install the Dr Nic’s Magic Models gem you can run the following command to fetch the gem remotely from RubyForge: <pre> gem install dr_nic_magic_models </pre>

or “download the gem manually”:rubyforge.org/projects/magicmodels and run the above command in the download directory.

Now you need to require the gem into your Ruby/Rails app. Insert the following line into your script (use config/environment.rb for your Rails apps):

<pre> require ‘dr_nic_magic_models’ </pre>

Your application is now blessed with magical mystery.

h2. David Copperfield eat your Ruby-crusted heart out

Let’s demonstrate the magical mystery in all its full-stage glory. Create a Ruby on Rails app (example uses sqlite3, but use your favourite databas):

<pre syntax=“ruby”> rails magic_show -d sqlite3 cd magic_show ruby script/generate model Person ruby script/generate model Group ruby script/generate model Membership </pre>

Update the migration 001_create_people.rb with: <pre syntax=“ruby”> class CreatePeople < ActiveRecord::Migration

def self.up
  create_table :people do |t|
    t.column :firstname, :string, :null => false
    t.column :lastname, :string, :null => false
    t.column :email, :string, :null => false
  end
end

def self.down
  drop_table :people
end

end </pre>

Similarly, update the def self.up method of 002_create_groups.rb with: <pre syntax=“ruby”>

create_table :groups do |t|
  t.column :name, :string, :null => false
  t.column :description, :string
end

</pre>

and 003_create_memberships.rb with: <pre syntax=“ruby”>

create_table :memberships do |t|
  t.column :person_id, :integer, :null => false
  t.column :group_id, :integer, :null => false
end

</pre>

And run your migrations to create the three tables: <pre> rake db:migrate </pre>

h3. And now for some “woofle dust”:en.wikipedia.org/wiki/List_of_conjuring_terms …

At the end of config/environment.rb add the following line:

<pre> require ‘dr_nic_magic_models’ </pre>

Now, let’s do a magic trick. First, let’s check our model classes (app/models/person.rb etc):

<pre syntax=“ruby”> class Person < ActiveRecord::Base end class Group < ActiveRecord::Base end class Membership < ActiveRecord::Base end </pre>

Nothing suspicious here. We have no validations and no associations. Just some plain old model classes.

UPDATE: To turn on magic validations, you now need to invoke generate_validations on defined classes. So, update your model classes:

<pre syntax=“ruby”> class Person < ActiveRecord::Base

generate_validations

end class Group < ActiveRecord::Base

generate_validations

end class Membership < ActiveRecord::Base

generate_validations

end </pre>

For this trick, we’ll need an ordinary console session. Any old one lying around the house will do.

<pre> ruby script/console </pre>

Now a normal model class is valid until you explicitly add validates_xxx commands. With Dr Nic’s Magic Models:

<pre syntax=“ruby”> person = Person.new

> #<Person:0x393e0f8 @attributes=“firstname”=>“”, “email”=>“”, @new_record=true>

person.valid?

> false

person.errors

> #<ActiveRecord::Errors:0x3537b38 @errors=

“firstname”=>[“can’t be blank”, “is too long (maximum is 255 characters)”], “lastname”=>[“can’t be blank”, “is too long (maximum is 255 characters)”], “email”=>[“can’t be blank”, “is too long (maximum is 255 characters)”], @base=#<Person:0x3538bf0 @errors=#<ActiveRecord::Errors:0x3537b38 …>, @new_record=true, @attributes=“firstname”=>nil, “email”=>nil>> </pre>

Kapoow! Instant validation! (NOTE: not as instant as it used to be - remember - you need to call generate_validations on each class as required)

Because you specified the three columns as :null => false, your ActiveRecord models will now automagically generated validates_presence_of for each non-null field, plus several other validations (since version 0.8.0).

Ok, we’re just warming up.

Your models normally require association commands (has_many, belongs_to, etc, as demonstrated above) to have the brilliantly simple support that Rails/ActiveRecords are known for.

Let’s just watch what Dr Nic’s Magic Models can do without any effort at all…

<pre syntax=“ruby”> person = Person.create(:firstname => “Nic”, :lastname => “Williams”, :email => “[email protected]”) group = Group.create(:name => “Magic Models Forum”, :description => “groups.google.com/magicmodels”) membership = Membership.create(:person => person, :group => group) person.memberships.length

> 1

membership.person

> <Person:0x38898e8 @attributes=“firstname”=>“Nic”,

“id”=>“1”, “email”=>“[email protected]”> group.memberships

> [<Membership:0x3c8cd70 @attributes=“id”=>“1”, “person_id”=>“1”>]

</pre>

The final association trick is a ripper. Automatic generation of has_many :through associations…

<pre syntax=“ruby”> >> person.groups

> [<Group:0x39047e0 @attributes=Models Forum”, “id”=>“1”, “description”=>nil>]

>> group.people

> [<Person:0x3c33580 @attributes=“firstname”=>“Nic”,

“id”=>“1”, “email”=>“[email protected]”>] </pre>

h3. Drum roll…

Ladies and gentlemen. For my final feat of magical mastery, I’ll ask you to do something you’ve never done before. This illusion is akin to the “floating lady”:www.toytent.com/Posters/985.html illusion that has been passed down through generations of magicians.

Exit your console session.

DELETE your three model classes: person.rb, group.rb, and membership.rb from the app/models folder. (You can always get them back via the model generator… be fearless!)

<pre>rm app/models/*.rb</pre>

Re-launch your console.

*drums are still rolling…*

Be prepared to applaud loudly…

<pre syntax=“ruby”> >> Person

> Person

</pre>

You applaud loudly, but watch for more…

<pre syntax=“ruby”> >> Person.new.valid?

> false

>> person = Person.find(1)

> <Person:0x3958930 @attributes=“firstname”=>“Nic”,

“id”=>“1”, “email”=>“[email protected]”> >> person.valid?

> true

>> person.memberships

> [<Membership:0x393a000 @attributes=“id”=>“1”, “person_id”=>“1”>]

>> person.groups

> [<Group:0x390df60 @attributes=Models Forum”, “id”=>“1”, “description”=>nil>]

</pre>

h3. Tada!

The end.

h3. Use modules to scope your magic

Only want to pick up tables starting with blog_?

<pre syntax=“ruby”>module Blog

magic_module :table_name_prefix => 'blog_'

end

Blog::Post.table_name # => ‘blog_posts’ </pre>

h2. Dr Nic’s Blog

“www.drnicwilliams.com”:www.drnicwilliams.com - for future announcements and other stories and things.

h2. Articles about Magic Models

h2. Forum

“groups.google.com/group/magicmodels”:groups.google.com/group/magicmodels

h2. Licence

This code is free to use under the terms of the MIT licence.

h2. Contact

Comments are welcome. Send an email to “Dr Nic Williams”:[email protected] or via his blog at “www.drnicwilliams.com”:www.drnicwilliams.com