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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|
Merge docrails: commit e6afd8b2736364322b673bbdcca3e9b38b6d3da0 Author: Xavier Noria <fxn@hashref.com> Date: Thu May 8 23:49:36 2008 +0200 Overall documentation improvement and markup corrections. Zillion changes. commit 2fead68b3192332eee27945ed95a94a64ca73f70 Author: Austin Putman <austin@emmanuel.local> Date: Wed May 7 19:35:46 2008 -0700 Documented class methods on ActionController::Routing. These are dangerous, and mostly used for testing. commit f5b84182dbc39bea79c8ee319c688d00fa99f9d1 Author: Teflon Ted <github@rudiment.net> Date: Wed May 7 16:08:49 2008 -0400 Added explanation about errant inflections not being patched in the future in order to avoid breaking legacy applications. commit 370f4f51722cec49ace17093d29e9ce9e8f15cfb Author: Sunny Ripert <negatif@gmail.com> Date: Wed May 7 14:00:59 2008 +0200 Applied list conventions in AR::Base commit 5bd18429f09d44e75191bec42a6db04bd33f3030 Author: Sunny Ripert <negatif@gmail.com> Date: Wed May 7 13:53:35 2008 +0200 Renamed Options list to Attributes list whenever they weren't option hashes in AR::Base commit d912bd5672316454457ae83f6e9dda5197beeb6f Author: Yaroslav Markin <yaroslav@markin.net> Date: Wed May 7 13:50:28 2008 +0400 Add a filter_parameter_logging usage hint to generated ApplicationController. This may help to remind the developer to filter sensitive information from application logs. Closes #11578 commit b243de0db3c2605121e055079854af5090d06374 Author: Jack Danger Canty <git@6brand.com> Date: Tue May 6 23:39:47 2008 -0700 doc: disambiguating an example ActiveRecord class commit f81d771f0657ae8375b84a77a059812cce5d6fd9 Author: Jack Danger Canty <git@6brand.com> Date: Tue May 6 23:35:05 2008 -0700 doc: ActiveRecord::Reflection::AssociationReflection#through_reflection Added documentation demonstrating the use of #through_reflection for finding intervening reflection objects for HasManyThrough and HasOneThrough. commit ae6b46f00b5b8b2939c6b37ce3329c83de7e71db Author: Cheah Chu Yeow <chuyeow@gmail.com> Date: Wed May 7 13:47:41 2008 +0800 Document AttributeAssignmentError and MultiparameterAssignmentErrors. commit 8f463550b597db2156b67733f31aed13487fbc3a Author: John Barnette <jbarnette@gmail.com> Date: Tue May 6 22:46:44 2008 -0700 Killing/fixing a bunch of outdated language in the AR README. commit aca44bcd92ef783abdf484b58abdde6786db0f89 Author: Cheah Chu Yeow <chuyeow@gmail.com> Date: Wed May 7 13:34:52 2008 +0800 Make a note about ActiveResource::Timeouterror being raised when ARes calls timeout. commit 284a930a93fbee16e25d06392779dbf2f03e9e12 Author: Jonathan Dance <jd@wuputah.com> Date: Tue May 6 14:58:26 2008 -0400 improvements to the page caching docs commit 9482da621390c874da7c921c8bd6230caae7035a Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 18:13:40 2008 +0200 validates_numericality_of() "integer" option really is "only_integer" commit e9afd6790a8f530528f6597a7f59bb283be754f6 Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 12:11:59 2008 +0200 Harmonized hash notation in AR::Base commit 67ebf14a91ffd970b582be4ff2991d691a9cf3e1 Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 12:06:19 2008 +0200 Turned options into rdoc-lists in AR::Base commit 0ec7c0a41d889d4e5382b9dff72f1aaba89bf297 Author: Marshall Huss <mwhuss@Macbook.local> Date: Sun May 4 23:21:33 2008 -0400 Added information of how to set element_name in the case the user has a name confliction with an existing model Signed-off-by: Pratik Naik <pratiknaik@gmail.com>
2008-05-09 05:38:02 -04:00
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
Merge docrails: commit e6afd8b2736364322b673bbdcca3e9b38b6d3da0 Author: Xavier Noria <fxn@hashref.com> Date: Thu May 8 23:49:36 2008 +0200 Overall documentation improvement and markup corrections. Zillion changes. commit 2fead68b3192332eee27945ed95a94a64ca73f70 Author: Austin Putman <austin@emmanuel.local> Date: Wed May 7 19:35:46 2008 -0700 Documented class methods on ActionController::Routing. These are dangerous, and mostly used for testing. commit f5b84182dbc39bea79c8ee319c688d00fa99f9d1 Author: Teflon Ted <github@rudiment.net> Date: Wed May 7 16:08:49 2008 -0400 Added explanation about errant inflections not being patched in the future in order to avoid breaking legacy applications. commit 370f4f51722cec49ace17093d29e9ce9e8f15cfb Author: Sunny Ripert <negatif@gmail.com> Date: Wed May 7 14:00:59 2008 +0200 Applied list conventions in AR::Base commit 5bd18429f09d44e75191bec42a6db04bd33f3030 Author: Sunny Ripert <negatif@gmail.com> Date: Wed May 7 13:53:35 2008 +0200 Renamed Options list to Attributes list whenever they weren't option hashes in AR::Base commit d912bd5672316454457ae83f6e9dda5197beeb6f Author: Yaroslav Markin <yaroslav@markin.net> Date: Wed May 7 13:50:28 2008 +0400 Add a filter_parameter_logging usage hint to generated ApplicationController. This may help to remind the developer to filter sensitive information from application logs. Closes #11578 commit b243de0db3c2605121e055079854af5090d06374 Author: Jack Danger Canty <git@6brand.com> Date: Tue May 6 23:39:47 2008 -0700 doc: disambiguating an example ActiveRecord class commit f81d771f0657ae8375b84a77a059812cce5d6fd9 Author: Jack Danger Canty <git@6brand.com> Date: Tue May 6 23:35:05 2008 -0700 doc: ActiveRecord::Reflection::AssociationReflection#through_reflection Added documentation demonstrating the use of #through_reflection for finding intervening reflection objects for HasManyThrough and HasOneThrough. commit ae6b46f00b5b8b2939c6b37ce3329c83de7e71db Author: Cheah Chu Yeow <chuyeow@gmail.com> Date: Wed May 7 13:47:41 2008 +0800 Document AttributeAssignmentError and MultiparameterAssignmentErrors. commit 8f463550b597db2156b67733f31aed13487fbc3a Author: John Barnette <jbarnette@gmail.com> Date: Tue May 6 22:46:44 2008 -0700 Killing/fixing a bunch of outdated language in the AR README. commit aca44bcd92ef783abdf484b58abdde6786db0f89 Author: Cheah Chu Yeow <chuyeow@gmail.com> Date: Wed May 7 13:34:52 2008 +0800 Make a note about ActiveResource::Timeouterror being raised when ARes calls timeout. commit 284a930a93fbee16e25d06392779dbf2f03e9e12 Author: Jonathan Dance <jd@wuputah.com> Date: Tue May 6 14:58:26 2008 -0400 improvements to the page caching docs commit 9482da621390c874da7c921c8bd6230caae7035a Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 18:13:40 2008 +0200 validates_numericality_of() "integer" option really is "only_integer" commit e9afd6790a8f530528f6597a7f59bb283be754f6 Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 12:11:59 2008 +0200 Harmonized hash notation in AR::Base commit 67ebf14a91ffd970b582be4ff2991d691a9cf3e1 Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 12:06:19 2008 +0200 Turned options into rdoc-lists in AR::Base commit 0ec7c0a41d889d4e5382b9dff72f1aaba89bf297 Author: Marshall Huss <mwhuss@Macbook.local> Date: Sun May 4 23:21:33 2008 -0400 Added information of how to set element_name in the case the user has a name confliction with an existing model Signed-off-by: Pratik Naik <pratiknaik@gmail.com>
2008-05-09 05:38:02 -04:00
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.
Merge docrails: commit e6afd8b2736364322b673bbdcca3e9b38b6d3da0 Author: Xavier Noria <fxn@hashref.com> Date: Thu May 8 23:49:36 2008 +0200 Overall documentation improvement and markup corrections. Zillion changes. commit 2fead68b3192332eee27945ed95a94a64ca73f70 Author: Austin Putman <austin@emmanuel.local> Date: Wed May 7 19:35:46 2008 -0700 Documented class methods on ActionController::Routing. These are dangerous, and mostly used for testing. commit f5b84182dbc39bea79c8ee319c688d00fa99f9d1 Author: Teflon Ted <github@rudiment.net> Date: Wed May 7 16:08:49 2008 -0400 Added explanation about errant inflections not being patched in the future in order to avoid breaking legacy applications. commit 370f4f51722cec49ace17093d29e9ce9e8f15cfb Author: Sunny Ripert <negatif@gmail.com> Date: Wed May 7 14:00:59 2008 +0200 Applied list conventions in AR::Base commit 5bd18429f09d44e75191bec42a6db04bd33f3030 Author: Sunny Ripert <negatif@gmail.com> Date: Wed May 7 13:53:35 2008 +0200 Renamed Options list to Attributes list whenever they weren't option hashes in AR::Base commit d912bd5672316454457ae83f6e9dda5197beeb6f Author: Yaroslav Markin <yaroslav@markin.net> Date: Wed May 7 13:50:28 2008 +0400 Add a filter_parameter_logging usage hint to generated ApplicationController. This may help to remind the developer to filter sensitive information from application logs. Closes #11578 commit b243de0db3c2605121e055079854af5090d06374 Author: Jack Danger Canty <git@6brand.com> Date: Tue May 6 23:39:47 2008 -0700 doc: disambiguating an example ActiveRecord class commit f81d771f0657ae8375b84a77a059812cce5d6fd9 Author: Jack Danger Canty <git@6brand.com> Date: Tue May 6 23:35:05 2008 -0700 doc: ActiveRecord::Reflection::AssociationReflection#through_reflection Added documentation demonstrating the use of #through_reflection for finding intervening reflection objects for HasManyThrough and HasOneThrough. commit ae6b46f00b5b8b2939c6b37ce3329c83de7e71db Author: Cheah Chu Yeow <chuyeow@gmail.com> Date: Wed May 7 13:47:41 2008 +0800 Document AttributeAssignmentError and MultiparameterAssignmentErrors. commit 8f463550b597db2156b67733f31aed13487fbc3a Author: John Barnette <jbarnette@gmail.com> Date: Tue May 6 22:46:44 2008 -0700 Killing/fixing a bunch of outdated language in the AR README. commit aca44bcd92ef783abdf484b58abdde6786db0f89 Author: Cheah Chu Yeow <chuyeow@gmail.com> Date: Wed May 7 13:34:52 2008 +0800 Make a note about ActiveResource::Timeouterror being raised when ARes calls timeout. commit 284a930a93fbee16e25d06392779dbf2f03e9e12 Author: Jonathan Dance <jd@wuputah.com> Date: Tue May 6 14:58:26 2008 -0400 improvements to the page caching docs commit 9482da621390c874da7c921c8bd6230caae7035a Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 18:13:40 2008 +0200 validates_numericality_of() "integer" option really is "only_integer" commit e9afd6790a8f530528f6597a7f59bb283be754f6 Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 12:11:59 2008 +0200 Harmonized hash notation in AR::Base commit 67ebf14a91ffd970b582be4ff2991d691a9cf3e1 Author: Sunny Ripert <negatif@gmail.com> Date: Mon May 5 12:06:19 2008 +0200 Turned options into rdoc-lists in AR::Base commit 0ec7c0a41d889d4e5382b9dff72f1aaba89bf297 Author: Marshall Huss <mwhuss@Macbook.local> Date: Sun May 4 23:21:33 2008 -0400 Added information of how to set element_name in the case the user has a name confliction with an existing model Signed-off-by: Pratik Naik <pratiknaik@gmail.com>
2008-05-09 05:38:02 -04:00
For other information, feel free to ask on the rubyonrails-talk
(http://groups.google.com/group/rubyonrails-talk) mailing list.