Setting Default Role using Enum based on Project creation

I have a Projects and a Relationships model to establish a 'following' relationship between a user and a project. I established three roles for the 'Relationship' using enum in the relationship model...they are admin, collaborator, and visitor. I need, however, to set the default role based upon the way in which the Relationship between user and project is established. The following simple scenarios are needed:

(a) A user who creates a project is automatically following the project...the Relationship role should be set to 'Admin' upon creation of the project

(b) if a visitor to the site simply navigates to a project profile page, they can click the 'Follow' button to establish a following relationship...however this should set the Relationship role to 'Visitor'

Relationship Model:

class Relationship < ActiveRecord::Base
  belongs_to :follower, class_name: "User"
  belongs_to :followed, class_name: "Project"
  validates :follower_id, presence: true
  validates :followed_id, presence: true

  enum role: [:admin, :collaborator, :visitor]
  after_initialize :set_default_role, :if => :new_record?

  def set_default_role
    self.role ||= :admin
  end
end

Relationships Controller:

class RelationshipsController < ApplicationController
  before_filter :authenticate_user!

  def create
    @project = Project.find(params[:relationship][:followed_id])
    current_user.follow!(@project)
    # relationship.visitor! View railsapps documentation for devise pundit#roles
    redirect_to @project
  end

  def destroy
    @project = Project.find(params[:id]).followed
    current_user.unfollow!(@project)
    redirect_to @project
  end

  private

  def relationship_params
    params.require(:relationship).permit(:followed_id, :follower_id)
  end

Projects Controller

class ProjectsController < ApplicationController
  before_filter :authenticate_user!, only: [:create, :new, :edit, :update, :delete, :followers]

def create
    @project = current_user.own_projects.build(project_params)
    if @project.save
      if params[:project][:projectimage].present?
        render :crop
      else
        flash[:success] = "You've successfully created a project..."
        redirect_to @project
      end
    else
      render 'new'
    end
  end

  def update
    @project = Project.find(params[:id])
    if @project.update_attributes(project_params)
      if params[:project][:projectimage].present?
        render :crop
      else
        flash[:success] = "Project Created"
        redirect_to @project
        @project.followers << current_user #this establishes the following relationship as soon as a new project is created between user/project
      end
    else
      render 'edit'
    end
  end

end

What would I need to change in my code in order to set the default role to either 'admin' or 'visitor' based on the two scenarios mentioned above?