When are associated objects saved ?
2006-07-25
A friend of mine asked me a question today. He wanted to know “When are associated objects saved” ?
See ActiveRecord::Associations. Look for the section titled “Unsaved objects and associations”.
Asymmetric associations
2006-02-15
In Rails, there are no requirements that both sides of an association be symmetric. In fact, I often find it useful to have asymmetric relationships.
For example, I’m building a mass-mailer. I have parties (people), emails and recipients. Emails are habtm with regards to parties. Since my join table contains other fields besides the two foreign keys, I need a real model for it.
Examine the following code:
1 class Email < ActiveRecord::Base
2 has_many :recipients
3 end
4
5 class Party < ActiveRecord::Base
6 has_and_belongs_to_many :emails,
7 :join_table => ‘recipients’
8 end
9
10 class Recipient < ActiveRecord::Base
11 belongs_to :email
12 belongs_to :party
13
14 def read!
15 self.toggle!(:read)
16 end
17 end
The above models give rise to the following very natural code:
1 >> fbos = Party.find_by_login(‘fbos’)
2 => #<Party:0×3c019d0 …>
3 >> info = Email.create(:subject => ‘Latest Schedule’,
4 :body => ‘Group schedule: …’)
5 => #<Email:0×3bece38 …>
6 >> info.recipients.create(:party => fbos)
7 => #<Recipient:0×3bccfd8 …>
8 >> fbos.emails
9 => [#<Email:0×3b80dc0 …>]
If access to read or unread E-Mail is needed, the habtm association can be declared more than once, with conditions that discriminate between the different states:
1 class Party < ActiveRecord::Base
2 has_and_belongs_to_many :unread_emails,
3 :join_table => ‘recipients’,
4 :conditions => ‘read = 0’
5 has_and_belongs_to_many :read_emails,
6 :join_table => ‘recipients’,
7 :conditions => ‘read = 1’
8 end
Please comment or send me an E-Mail at francois.beausoleil@gmail.com to tell me about your experiences with asymmetric relationships.
