Initial import.

git-svn-id: svn+ssh://svn0.sea.apvio.net/home/rwl4/inherits_from@1 bd10a536-b517-0410-99c0-c9a68740b5c0

README

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+InheritsFrom
+============
+
+Allows class inheritance with ActiveRecord.
+
+It is very basic at the moment, and might even be fundamentally flawed.

Rakefile

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+require 'rake'
+require 'rake/testtask'
+require 'rake/rdoctask'
+
+desc 'Default: run unit tests.'
+task :default => :test
+
+desc 'Test the inherits_from plugin.'
+Rake::TestTask.new(:test) do |t|
+  t.libs << 'lib'
+  t.pattern = 'test/**/*_test.rb'
+  t.verbose = true
+end
+
+desc 'Generate documentation for the inherits_from plugin.'
+Rake::RDocTask.new(:rdoc) do |rdoc|
+  rdoc.rdoc_dir = 'rdoc'
+  rdoc.title    = 'InheritsFrom'
+  rdoc.options << '--line-numbers' << '--inline-source'
+  rdoc.rdoc_files.include('README')
+  rdoc.rdoc_files.include('lib/**/*.rb')
+end

init.rb

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+require 'inherits_from'

lib/inherits_from.rb

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+require 'active_record'
+
+# +inherits_from+ is an +ActiveRecord+ plugin designed to allow simple multiple table (class) inheritance.
+# 
+# Example:
+#   class Product < ActiveRecord::Base
+#     inherits_from :product
+#   end
+#
+#   class Book < ActiveRecord::Base
+#     inherits_from :product
+#   end
+#
+#   class Video < ActiveRecord::Base
+#     inherits_from :product
+#   end
+#
+#   book = Book.find(1)
+#   book.name => "Agile Development with Rails"
+#   book.author => "Dave Thomas"
+#
+#   video = Video.find(2)
+#   book.name => "Twilight Zone Season 1"
+#   book.actors => "Rod Serling"
+
+class ActiveRecord::Base
+  attr_reader :reflection
+
+  # Creates an inheritance association and generates proxy methods in the inherited object for easy access to the parent.
+  # Currently, the options are ignored.
+  #
+  # Example:
+  #   class Book < ActiveRecord::Base
+  #     inherits_from :product
+  #   end
+  def self.inherits_from(association_id, options = {})
+    belongs_to association_id
+
+    reflection = create_reflection(:belongs_to, association_id, options, self)
+
+    association_class = Object.const_get(reflection.class_name)
+
+    inherited_column_names = association_class.column_names.reject { |c| self.column_names.grep(c).length > 0 || c == "type"}
+
+    inherited_column_names.each { |name| alias_associated_attr(association_id, name) }
+
+    before_callback = <<-end_eval
+      init_inherited("#{association_id}")
+      instance_variable_get("@#{association_id}").save
+    end_eval
+
+    before_create(before_callback)
+    before_update(before_callback)
+  end
+
+  # Creates a proxy accessor method for an inherited object.
+  def self.alias_associated_attr(association_id, name)
+    define_method(name) do
+      init_inherited_assoc(association_id)
+      klass = send(association_id)
+
+      klass.send(name)
+    end
+
+    define_method("#{name}=") do |new_value|
+      init_inherited_assoc(association_id)
+      klass = send(association_id)
+
+      klass.send("#{name}=", new_value)
+    end
+  end
+
+  private
+  # Ensures that there is an association to access, if not, creates one.
+  def init_inherited_assoc(association_id)
+    if new_record? and instance_variable_get("@#{association_id}").nil?
+      send("build_#{association_id}")
+      instance_variable_get("@#{association_id}").type = self.class.to_s
+    end
+  end
+end

test/fixtures/book.rb

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+class Book < ActiveRecord::Base
+  inherits_from :product
+
+  validates_presence_of :name, :price, :pages
+end

test/fixtures/books.yml

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+agile_book: 
+  author: Dave Thomas
+  product_id: 1
+  id: 1
+  pages: 300

test/fixtures/product.rb

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+class Product < ActiveRecord::Base
+  validates_presence_of :name
+end

test/fixtures/products.yml

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+agile_book: 
+  name: Agile Web Development with Rails
+  price: 2995
+  type: Book
+  id: 1
+twilight_video: 
+  name: Twilight Zone Season 1
+  price: 8945
+  type: Video
+  id: 2

test/fixtures/video.rb

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+class Video < ActiveRecord::Base
+  inherits_from :product
+
+  validates_presence_of :name, :price, :minutes, :starring
+end

test/fixtures/videos.yml

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+twilight_video: 
+  minutes: 490
+  product_id: 2
+  id: 1
+  starring: Rod Serling

test/inherits_from_test.rb

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+require 'test/unit'
+
+class InheritsFromTest < Test::Unit::TestCase
+  def test_code_needs_to_be_written
+    flunk "Anyone care to write some tests for me? ActiveRecord tests are painful."
+  end
+end