Rails 4 has_many :through relationship: assign default value to join model attribute on create action from parent model

I have three models:

class User < ActiveRecord::Base
  has_many :administrations
  has_many :calendars, through: :administrations
end

class Calendar < ActiveRecord::Base
  has_many :administrations
  has_many :users, through: :administrations
end

class Administration < ActiveRecord::Base
  belongs_to :user
  belongs_to :calendar
end

Remark: I am using Devise for authentication on the User model.

The join Administration model has the following attributes:

• id
• user_id
• calendar_id
• role

Here are my current routes:

devise_for :users, :path => 'account'

resources :users do
  resources :calendars
end

And here is my calendars_controller:

class CalendarsController < ApplicationController
  before_action :set_calendar, only: [:show, :edit, :update, :destroy]
  before_action :authenticate_user!

  # GET /calendars
  # GET /calendars.json
  def index
    @user = current_user
    @calendars = Calendar.all
  end

  # GET /calendars/1
  # GET /calendars/1.json
  def show
    @user = current_user
    @calendar = Calendar.find(params[:id])
  end

  # GET /calendars/new
  def new
    @user = current_user
    @calendar = @user.calendars.new
  end

  # GET /calendars/1/edit
  def edit
    @user = current_user
  end

  # POST /calendars
  # POST /calendars.json
  def create
    @user = current_user
    @calendar = @user.calendars.new(calendar_params)

    respond_to do |format|
      if @calendar.save
        format.html { redirect_to user_calendar_path(@user,@calendar), notice: 'Calendar was successfully created.' }
        format.json { render :show, status: :created, location: @calendar }
      else
        format.html { render :new }
        format.json { render json: @calendar.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /calendars/1
  # PATCH/PUT /calendars/1.json
  def update
    @user = current_user
    @calendar = Calendar.find(params[:id])
    respond_to do |format|
      if @calendar.update(calendar_params)
        format.html { redirect_to user_calendar_path(@user,@calendar), notice: 'Calendar was successfully updated.' }
        format.json { render :show, status: :ok, location: @calendar }
      else
        format.html { render :edit }
        format.json { render json: @calendar.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /calendars/1
  # DELETE /calendars/1.json
  def destroy
    @user = current_user
    @calendar.destroy
    respond_to do |format|
      format.html { redirect_to user_calendars_url, notice: 'Calendar was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_calendar
      @calendar = Calendar.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def calendar_params
      params.require(:calendar).permit(:name)
    end
end

My basic CRUD actions are working: once a user is logged in, he can create, show, edit and destroy a calendar that belongs to him.

What I am trying to figure out now, is how to define a default role — Owner — in the Administration join table when a user creates a new calendar.

I was considering adding the following line of code to Calendars#Create:

current_user.add_calendar_and_role(@calendar.id, 'Owner')

but I am not sure this is a good practice.

Instead, shouldn't I define a make_owner method in my administration model and use it with a callback in the Calendars#Create action?

Should I also implement accepts_nested_attributes_for in my calendar model?

Or is there an even better solution that I am forgetting about?