On 7 December 2013 19:23, John Merlino <stoici...@aol.com> wrote: > self-joins are discussed here: > http://guides.rubyonrails.org/association_basics.html#self-joins > > self-referential association is discussed here: > http://railscasts.com/episodes/163-self-referential-association > > The main difference I see is that self-referential association creates a > join model, such as friendship, which links another model, such as user, to > itself, so a user can have many friends (which are other users), and a > friend can be befriended by a user. The self-joins looks like there is no > join model. Simply a foreign key is added to the same model, such as a > manager_id column to the employee model. An employee, who is a manager, can > have many other employees, who are subordinates. And the link is done on the > same table itself, association the employee manager_id column with the the > employee id column. To me, these two techniques look virtually the same. Is > there a difference and which is preferred?
With a join model the relationship is symetrical. Each user can have many friends and can be the friend of many other users, similar to a has_and_belongs_to_many association. With the self referential association you describe, a manager can have many employees but an employee can belongs to only one manager (like a has_many, belongs_to association). So which one to use depends on the requirements. Colin -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-talk+unsubscr...@googlegroups.com. To post to this group, send email to rubyonrails-talk@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/rubyonrails-talk/CAL%3D0gLuOKFb3e4JVoyTtkH0SJDurPSsxSXRwsjsGnPRWXy4pHQ%40mail.gmail.com. For more options, visit https://groups.google.com/groups/opt_out.
