在轨道中将self.id与嵌套模型before_create关联

Question

I have my models & associations currently setup like so:

class User < ActiveRecord::Base
  has_and_belongs_to_many :projects
  has_many :versions, :through => :projects
end

class Projects < ActiveRecord::Base
  has_many :versions
end

class Version < ActiveRecord::Base
  belongs_to :project
  attr_accessible :user_id, :project_id
  before_create :associate_user

 def associate_user
  # I have no idea what to do here - in fact, I don't think this is even the right place to do this!
 end
end

When I do something like user.projects.first.versions.create , I would like the user_id field in Version to be filled with the user_id of the user through whom the model was created. Right now, when I execute that create method, it is set to nil. Now, this makes sense, and I understand why it doesnt work. I just cant figure out how to make this work.

I've been scratching my head over this, and cannot figure it out! How would you accomplish this?

UPDATE

Note: although this worked, Levi's answer below is a much, much better solution, and is what I ended up going with

I figured it out, but I would still like feedback on whether this is the best way to go about this. I feel like there may be a built-in method to rails to do this that I'm missing

Here's my updated Version model:

class Version < ActiveRecord::Base
belongs_to :production
attr_accessible :user_id, :production_id

after_create :associate_user

def associate_user
    @users = User.all(:include => :productions, :conditions => {"productions_users.production_id" => self.production_id})
    @users.each do |user|
        user.productions.each do |production|
            if production.versions.exists?(self)
                @version_user = user
            end
        end
    end
    self.user_id = @version_user.id
 end
end

Answer 1

I would just pass the id in when you create the version.

user.projects.first.version.create(:user_id => user.id)

That way you don't need the before_create callback at all.

Edit:

You may also want to consider your database structure. You have a project_id and a user_id on your versions table. You also have the join table ( projects_users ) with the same keys. Why not turn that into a real model and add a belongs_to :user_project (or whatever is appropriate) to the Version model? That is one extra join to go from Versions to Projects, but the data model makes more sense.

class User < ActiveRecord::Base
  has_many :user_projects
  has_many :projects, :through => :user_projects
  has_many :versions, :through => :projects
end

class UserProject < ActiveRecord::Base
  belongs_to :user
  belongs_to :project
  has_many :versions
end

class Projects < ActiveRecord::Base
  has_many :versions
  has_many :user_projects
  has_many :users, :through => :user_projects
end

class Version < ActiveRecord::Base
  belongs_to :user_project
end