Active Record associations question

Rails
1

Hi

Something I’m doing works magically in Rails and I’m trying to figure
out how :slight_smile:

Lets say I have a Post model which has many Comments

Within my Comment model I have this:

def foo(title)
self.create(:title => “title”)
end

Then I do this:
Post.find(4).foo(“hello”)

Rails creates a new Comment with a post_id of 6… How does it know to
do this!? Where does it get the correct post_id from?

This has really been puzzling me.

Thanks a lot
Ryan

2

On 6 Mar 2008, at 18:58, Ryan wrote:

def foo(title)
self.create(:title => “title”)
end

Then I do this:
Post.find(4).foo(“hello”)

Rails creates a new Comment with a post_id of 6… How does it know to
do this!? Where does it get the correct post_id from?

I assume that you meant to type Post.find(6).comments.foo(‘hello’)
In general any class method on a model will be available as a scoped
method on an association collection. The comments object is special:
it’s an association collection (not just a dumb) array, so it knows
that it belongs to that particular instance of post. If it doesn’t
know how to handle a method, it will just pass it on to the class
(here Comment) having previously scoped it (via with_scope)

Fred

3

Yeah, thats what I meant to type :slight_smile:

Thanks for the help

On Mar 7, 11:45 am, Frederick C. [email protected]