group creator transfered to other user if group creator leaves group

Question

First question: I have a group model that belongs_to :creator, :class_name => "User" and if the creator leaves I want someone else in the group to become the "creator". How would I do this?

As a second question, I would also like to give the leaving creator to choose a new creator when leaving, or let it be automatically assigned.

as of right now these are what my models look like:

class Group < ActiveRecord::Base

  belongs_to :creator, :class_name => "User"

  has_many :members, :through => :memberships
  has_many :memberships, :foreign_key => "new_group_id"

and my User model:

class User < ActiveRecord::Base

  has_many :groups, foreign_key: :creator_id

  has_many :memberships, foreign_key: :member_id
  has_many :new_groups, through: :memberships

As a third question, I would like the group to be destroyed when the creator leaves. How can I set up this kind of relation?

Answer 1

These are 3 questions, and the first two are quite open, so I'd try to answer all of them in order making some assumptions down the road.

First question

This depends on what do you want the behavior for choosing a new creator to be. Do you want it to be automatically assigned from the current members? Do you want to give other members to have the change to auto-assign themselves as creator? In the latter you need to provide your members a full UI (routes, controllers, views) for that purpose, so I'll show you how would I code the first option.

First, I'd encapsulate the group leaving logic into its own method on the Group model, that we'll use in the controller for this purpose. On Group we define the logic for assigning as new creator. The logic here will be to pass the method a new_creator if we have it, or default to the first of the members if not given.

class Group < ActiveRecord::Base
  def reassign(new_creator = nil)
    new_creator ||= members.first

    if new_creator
      self.creator = new_creator
      save
    else
      false
    end
  end
end

As an alternative approach, you can move this logic into an Observer (or any alternative) that will observe on Group model for the attribute creator_id to be nulled.

Second question

This one will involve a full UI that you'll need to figure out yourself according to your specifications. In short, I'd create a new action in your GroupsController for members to leave groups like this:

# config/routes.rb
resources :groups do
  member do 
    get :leave
    patch :reassign
  end
end

# app/controllers/groups_controller.rb
class GroupsController < ApplicationController
  def leave
    @group = Group.find(params[:id])
  end

  def reassign
    @group = Group.find(params[:id])
    if @group.reassign(params[:new_creator_id])
      redirect_to my_fancy_path
    else
      render :leave
    end 
  end
end

In your views you'll have your form_for @group with the new member candidates (possible with a select_tag :new_creator_id) and the rest of your UI as you prefer.

Third question

This is the easiest. You just define your association like this and you'll get all User groups destroyed after the user is deleted.

class User < ActiveRecord::Base
  has_many :groups, foreign_key: :creator_id, dependent: :destroy
end