Ruby Rails :has_many, autosetting a column

Question

Given the following Ruby-on-Rails code (1.8.6, 2.3.5):

class MyClass < ActiveRecord::Base
  has_many :modifiers,
    :conditions => ["affects_class = ?", self.name],
    :foreign_key => :affects_id
end

What I'm trying to do is to automatically set the affects_class column to 'MyClass'. In other words:

myInstance = MyClass.find(:first)
modifier = Modifier.new
modifier.affects_class = self.name # Don't want to have to do this
myInstance.modifiers << modifier

I don't want to have to set modifier.affects_class. After all, I don't have to set modifier.affects_id; that's set automatically by the has_many relation. Is there some option I can set on has_many? Or am I stuck having to set it each time?

Answer 1

Forgive me if what I'll say doesn't make any sense... but I can't test here what I'm about to suggest, so...

railsapi.doc says the following about the :conditions option on a has_many relation:

[...] Record creations from the association are scoped if a hash is used. has_many :posts, :conditions => {:published => true} will create published posts with @blog.posts.create or @blog.posts.build.

So, if you set up the condition using a hash

class MyClass < ActiveRecord::Base
   has_many :modifiers,
      :conditions => {:affects_class => self.name},
      :foreign_key => :affects_id
end

and create the modifiers using

myInstance = MyClass.find(:first)
myInstance.modifiers.create #or myInstance.modifiers.build

won't you get modifiers with the name already set?

I'm just not very confident about using self.name. I don't know if this is the right way to get the class' name.

Anyway, let me know if it works. It's new to me and very useful.