Defining tables and classes (using MySQL) in Ruby on Rails
By: David Heinemeier Hansson in Ruby Tutorials on 2009-03-03
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
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