How to create Rails models with multiple complex associations/joins? - ruby-on-rails

Question

I am trying to figure out how to create ActiveRecord models with associations that can yield the same results as this SQL query:
SELECT login, first_name, last_name, email_address
FROM accounts
INNER JOIN people ON person.id = accounts.person_id
INNER JOIN email_address_people ON person.id = email_address_people.person_id
INNER JOIN email_addresses ON email_address.id = email_address_people.email_address_id
INNER JOIN email_address_types ON email_address_types.id = email_address_people.email_address_type_id
WHERE email_address_types.email_address_type = 'account';
The table structure is as follows, and assumes each table has an id per normal ActiveRecord convention:
accounts
id : int
person_id : int
login : string
people
id : int
first_name : string
last_name : string
email_address_people
id : int
person_id : int
email_address_id : int
email_address_type_id : int
email_addresses
id : int
email_address : string
email_address_types
id : int
email_address_type: string
I need the models to be fully functional, and not limited by things like :find_by_sql.
How do I create the associated models that make this possible?
Thanks!
Chris Benson
chris#chrisbenson.com

Answer 1

Try this:
Your model classes:
class EmailAddress < ActiveRecord::Base
end
class EmailAddressType < ActiveRecord::Base
end
class People < ActiveRecord::Base
has_many :accounts
has_many :email_address_people
has_many :email_addresses, :through => :email_address_people
has_many :account_email_address_people,
:class_name => "EmailAddressPeople",
:conditions => "email_address_type = 'account'"
has_many :account_email_addresses,
:through => :account_email_address_people
end
class EmailAddressPeople < ActiveRecord::Base
belongs_to :person
belongs_to :email_address
belongs_to :email_address_type
end
Your account model:
class Account < ActiveRecord::Base
belongs_to :person
# now to the actual method
def account_emails
person.account_email_addresses.map do |email|
[login, person.first_name, person.last_name, email.email_address]
end
end
# Brute force SQL if you prefer
def account_emails2
sql = "YOUR SQL HERE"
self.connection.select_values(sql)
end
end
Assuming you have the Account object in hand account.account_emails makes two database calls:
Get the person using a id
Get the account emails for the person
Going directly to the database(i.e. account.account_emails2) is the fastest option, but it is not the Rails way.

Answer 2

I think the best thing to do here is to give you the documentation first: http://railsbrain.com/api/rails-2.3.2/doc/index.html
Look up "has_many" (paying attention to :through) and "belongs_to", as well as "has_one", although I don't think you'll use the later.
This blog post will help you with the has_many :through concept -- and I think after that, you'll be set. Let us know if there's anything that's not clear!
class Account < ActiveRecord::Base
belongs_to :person
end
class Person < ActiveRecord::Base
has_many :accounts
has_many :email_addresses :through => :email_address_people
end
class EmailAddress < ActiveRecord::Base
belongs_to :email_address_type
belongs_to :person
has_one :email_address_type
end
class EmailAddressType < ActiveRecord::Base
has_many :email_addresses :through => :email_address_people
end
I would get started with that. It's not tested, but if we see what breaks, then we can fix it.. :)