mirror of
https://github.com/rails/rails.git
synced 2022-11-09 12:12:34 -05:00
351 lines
11 KiB
Text
351 lines
11 KiB
Text
= 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.
|