Msan Msan wrote in post #1061478: > I've noticed that if I use associations with has_many_and_belongs_to > and i call a destroy method on an object of the association, the > record in the join table is automatically deleted. > If I use has_many :though, for example: > > Category > has_many :categorizations > has_many :products, :through => :categorizations > > I have to put explicity > > has_many :categorization, :dependent => :destroy > > otherwise the association isn't deleted. > Why?
A HABTM B (to me) infers that the join table AB serves no purpose other than to link As and Bs. Without a specific A, the AB record has no meaning. So the HABTM specification lets Rails make the assumption that when A is deleted, the AB related to that A can be deleted as well. A has_many B A has_many C, through B implies (also to me) that joining through the intermediary table B is an artifact of the relationships between As, Bs, and Cs, and the entity modeled in B has value independent of its relationship between A and C. Like Project has_many :scenarios has_many :unittests, :through => :scenarios When a Project is deleted, I don't want all those Scenarios deleted... Unittest has_many :testings, :dependent => :destroy has_many :testresults, :through => :testings When a unittest is deleted, I delete all the testings (and testresults) since test results or testing instances aren't much use without the requirements (the unittest). -- Posted via http://www.ruby-forum.com/. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk@googlegroups.com. To unsubscribe from this group, send email to rubyonrails-talk+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
