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-= Active Record -- Object-relation mapping put on rails
-
-Active Record connects business objects and database tables to create a persistable
-domain model where logic and data are presented in one wrapping. It's an implementation
-of the object-relational mapping (ORM) pattern[http://www.martinfowler.com/eaaCatalog/activeRecord.html]
-by the same name as described by Martin Fowler:
-
- "An object that wraps a row in a database table or view, encapsulates
- the database access, and adds domain logic on that data."
-
-Active Record's main contribution to the pattern is to relieve the original of two stunting problems:
-lack of associations and inheritance. By adding a simple domain language-like set of macros to describe
-the former and integrating the Single Table Inheritance pattern for the latter, Active Record narrows the
-gap of functionality between the data mapper and active record approach.
-
-A short rundown of the major features:
-
-* Automated mapping between classes and tables, attributes and columns.
-
- class Product < ActiveRecord::Base; end
-
- ...is automatically mapped to the table named "products", such as:
-
- CREATE TABLE products (
- id int(11) NOT NULL auto_increment,
- name varchar(255),
- PRIMARY KEY (id)
- );
-
- ...which again gives Product#name and Product#name=(new_name)
-
- {Learn more}[link:classes/ActiveRecord/Base.html]
-
-
-* Associations between objects controlled by simple meta-programming macros.
-
- class Firm < ActiveRecord::Base
- has_many :clients
- has_one :account
- belongs_to :conglomorate
- end
-
- {Learn more}[link:classes/ActiveRecord/Associations/ClassMethods.html]
-
-
-* Aggregations of value objects controlled by simple meta-programming macros.
-
- class Account < ActiveRecord::Base
- composed_of :balance, :class_name => "Money",
- :mapping => %w(balance amount)
- composed_of :address,
- :mapping => [%w(address_street street), %w(address_city city)]
- end
-
- {Learn more}[link:classes/ActiveRecord/Aggregations/ClassMethods.html]
-
-
-* Validation rules that can differ for new or existing objects.
-
- class Account < ActiveRecord::Base
- validates_presence_of :subdomain, :name, :email_address, :password
- validates_uniqueness_of :subdomain
- validates_acceptance_of :terms_of_service, :on => :create
- validates_confirmation_of :password, :email_address, :on => :create
- end
-
- {Learn more}[link:classes/ActiveRecord/Validations.html]
-
-* Callbacks as methods or queues on the entire lifecycle (instantiation, saving, destroying, validating, etc).
-
- class Person < ActiveRecord::Base
- def before_destroy # is called just before Person#destroy
- CreditCard.find(credit_card_id).destroy
- end
- end
-
- class Account < ActiveRecord::Base
- after_find :eager_load, 'self.class.announce(#{id})'
- end
-
- {Learn more}[link:classes/ActiveRecord/Callbacks.html]
-
-
-* Observers for the entire lifecycle
-
- class CommentObserver < ActiveRecord::Observer
- def after_create(comment) # is called just after Comment#save
- Notifications.deliver_new_comment("david@loudthinking.com", comment)
- end
- end
-
- {Learn more}[link:classes/ActiveRecord/Observer.html]
-
-
-* Inheritance hierarchies
-
- class Company < ActiveRecord::Base; end
- class Firm < Company; end
- class Client < Company; end
- class PriorityClient < Client; end
-
- {Learn more}[link:classes/ActiveRecord/Base.html]
-
-
-* Transactions
-
- # Database transaction
- Account.transaction do
- david.withdrawal(100)
- mary.deposit(100)
- end
-
- {Learn more}[link:classes/ActiveRecord/Transactions/ClassMethods.html]
-
-
-* Reflections on columns, associations, and aggregations
-
- reflection = Firm.reflect_on_association(:clients)
- reflection.klass # => Client (class)
- Firm.columns # Returns an array of column descriptors for the firms table
-
- {Learn more}[link:classes/ActiveRecord/Reflection/ClassMethods.html]
-
-
-* Direct manipulation (instead of service invocation)
-
- So instead of (Hibernate[http://www.hibernate.org/] example):
-
- long pkId = 1234;
- DomesticCat pk = (DomesticCat) sess.load( Cat.class, new Long(pkId) );
- // something interesting involving a cat...
- sess.save(cat);
- sess.flush(); // force the SQL INSERT
-
- Active Record lets you:
-
- pkId = 1234
- cat = Cat.find(pkId)
- # something even more interesting involving the same cat...
- cat.save
-
- {Learn more}[link:classes/ActiveRecord/Base.html]
-
-
-* Database abstraction through simple adapters (~100 lines) with a shared connector
-
- ActiveRecord::Base.establish_connection(:adapter => "sqlite", :database => "dbfile")
-
- ActiveRecord::Base.establish_connection(
- :adapter => "mysql",
- :host => "localhost",
- :username => "me",
- :password => "secret",
- :database => "activerecord"
- )
-
- {Learn more}[link:classes/ActiveRecord/Base.html#M000081] and read about the built-in support for
- MySQL[link:classes/ActiveRecord/ConnectionAdapters/MysqlAdapter.html], PostgreSQL[link:classes/ActiveRecord/ConnectionAdapters/PostgreSQLAdapter.html], SQLite[link:classes/ActiveRecord/ConnectionAdapters/SQLiteAdapter.html], Oracle[link:classes/ActiveRecord/ConnectionAdapters/OracleAdapter.html], SQLServer[link:classes/ActiveRecord/ConnectionAdapters/SQLServerAdapter.html], and DB2[link:classes/ActiveRecord/ConnectionAdapters/DB2Adapter.html].
-
-
-* Logging support for Log4r[http://log4r.sourceforge.net] and Logger[http://www.ruby-doc.org/stdlib/libdoc/logger/rdoc]
-
- ActiveRecord::Base.logger = Logger.new(STDOUT)
- ActiveRecord::Base.logger = Log4r::Logger.new("Application Log")
-
-
-* Database agnostic schema management with Migrations
-
- class AddSystemSettings < ActiveRecord::Migration
- def self.up
- create_table :system_settings do |t|
- t.string :name
- t.string :label
- t.text :value
- t.string :type
- t.integer :position
- end
-
- SystemSetting.create :name => "notice", :label => "Use notice?", :value => 1
- end
-
- def self.down
- drop_table :system_settings
- end
- end
-
- {Learn more}[link:classes/ActiveRecord/Migration.html]
-
-== Simple example (1/2): Defining tables and classes (using MySQL)
-
-Data definitions are specified only in the database. Active Record queries the database for
-the column names (that then serves to determine which attributes are valid) on regular
-object instantiation through the new constructor and relies on the column names in the rows
-with the finders.
-
- # CREATE TABLE companies (
- # id int(11) unsigned NOT NULL auto_increment,
- # client_of int(11),
- # name varchar(255),
- # type varchar(100),
- # PRIMARY KEY (id)
- # )
-
-Active Record automatically links the "Company" object to the "companies" table
-
- class Company < ActiveRecord::Base
- has_many :people, :class_name => "Person"
- end
-
- class Firm < Company
- has_many :clients
-
- def people_with_all_clients
- clients.inject([]) { |people, client| people + client.people }
- end
- end
-
-The foreign_key is only necessary because we didn't use "firm_id" in the data definition
-
- class Client < Company
- belongs_to :firm, :foreign_key => "client_of"
- end
-
- # CREATE TABLE people (
- # id int(11) unsigned NOT NULL auto_increment,
- # name text,
- # company_id text,
- # PRIMARY KEY (id)
- # )
-
-Active Record will also automatically link the "Person" object to the "people" table
-
- class Person < ActiveRecord::Base
- belongs_to :company
- end
-
-== Simple example (2/2): Using the domain
-
-Picking a database connection for all the Active Records
-
- ActiveRecord::Base.establish_connection(
- :adapter => "mysql",
- :host => "localhost",
- :username => "me",
- :password => "secret",
- :database => "activerecord"
- )
-
-Create some fixtures
-
- firm = Firm.new("name" => "Next Angle")
- # SQL: INSERT INTO companies (name, type) VALUES("Next Angle", "Firm")
- firm.save
-
- client = Client.new("name" => "37signals", "client_of" => firm.id)
- # SQL: INSERT INTO companies (name, client_of, type) VALUES("37signals", 1, "Firm")
- client.save
-
-Lots of different finders
-
- # SQL: SELECT * FROM companies WHERE id = 1
- next_angle = Company.find(1)
-
- # SQL: SELECT * FROM companies WHERE id = 1 AND type = 'Firm'
- next_angle = Firm.find(1)
-
- # SQL: SELECT * FROM companies WHERE id = 1 AND name = 'Next Angle'
- next_angle = Company.find(:first, :conditions => "name = 'Next Angle'")
-
- next_angle = Firm.find_by_sql("SELECT * FROM companies WHERE id = 1").first
-
-The supertype, Company, will return subtype instances
-
- Firm === next_angle
-
-All the dynamic methods added by the has_many macro
-
- next_angle.clients.empty? # true
- next_angle.clients.size # total number of clients
- all_clients = next_angle.clients
-
-Constrained finds makes access security easier when ID comes from a web-app
-
- # SQL: SELECT * FROM companies WHERE client_of = 1 AND type = 'Client' AND id = 2
- thirty_seven_signals = next_angle.clients.find(2)
-
-Bi-directional associations thanks to the "belongs_to" macro
-
- thirty_seven_signals.firm.nil? # true
-
-
-== Philosophy
-
-Active Record attempts to provide a coherent wrapper as a solution for the inconvenience that is
-object-relational mapping. The prime directive for this mapping has been to minimize
-the amount of code needed to build a real-world domain model. This is made possible
-by relying on a number of conventions that make it easy for Active Record to infer
-complex relations and structures from a minimal amount of explicit direction.
-
-Convention over Configuration:
-* No XML-files!
-* Lots of reflection and run-time extension
-* Magic is not inherently a bad word
-
-Admit the Database:
-* Lets you drop down to SQL for odd cases and performance
-* Doesn't attempt to duplicate or replace data definitions
-
-
-== Download
-
-The latest version of Active Record can be found at
-
-* http://rubyforge.org/project/showfiles.php?group_id=182
-
-Documentation can be found at
-
-* http://ar.rubyonrails.com
-
-
-== Installation
-
-The prefered method of installing Active Record is through its GEM file. You'll need to have
-RubyGems[http://rubygems.rubyforge.org/wiki/wiki.pl] installed for that, though. If you have,
-then use:
-
- % [sudo] gem install activerecord-1.10.0.gem
-
-You can also install Active Record the old-fashioned way with the following command:
-
- % [sudo] ruby install.rb
-
-from its distribution directory.
-
-
-== License
-
-Active Record is released under the MIT license.
-
-
-== Support
-
-The Active Record homepage is http://www.rubyonrails.com. You can find the Active Record
-RubyForge page at http://rubyforge.org/projects/activerecord. And as Jim from Rake says:
-
- Feel free to submit commits or feature requests. If you send a patch,
- remember to update the corresponding unit tests. If fact, I prefer
- new feature to be submitted in the form of new unit tests.
-
-For other information, feel free to ask on the rubyonrails-talk
-(http://groups.google.com/group/rubyonrails-talk) mailing list.
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