Ruby on Rails

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).

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