create_job.rb

class CreateJob
  def initialize(params, user)
    @user = user
    @params = params
  end

  def run!
    create_job
  end


  private

  def create_job
    @user.create_job(job_params)
  end

  def job_params
    @params.require(:job).permit(:employer, :address, :address2, :city, :state, :zipcode, :contact)
  end


end

create_user.rb

class CreateUser
  def initialize(data)
    @user_params = data
  end

  def run!
    create_user
  end

  private

  def user_params
    @user_params.require(:user).permit(:first_name, :last_name, :email, :password, :team_id, :phone_number, :birthday, :business_industry_id, :business_category_id)
  end

  def create_user
    user = User.new(user_params)
    if user.save
      # create user job if successful
      true
    else
      # use this to flash error messages
      false
    end
  end

end

errror.log

1.2) Failure/Error: = form_for @user do |f|

    ActionView::Template::Error:
      First argument in form cannot contain nil or be empty

new.html.haml

#- users/new.html.haml
%h4
  Enter your information
= form_for @user do |f|
  = f.label :first_name
  = f.text_field :first_name
  = f.label :last_name
  = f.text_field :last_name

  %h4 login details into Bold Networking

  = f.label :email
  = f.text_field :email
  = f.label :password
  = f.password_field :password
  = fields_for :job do |job|
    %h4
      Your Employer /  Business name
    = job.label :employer
    = job.text_field :employer

    %h4
      please select a your business category
    = select_tag "business_category", options_from_collection_for_select(BusinessCategory.all, "id", "name"), prompt: "Please select a Business Category"
    = select_tag "user[business_industry_id]", options_for_select([])

    %h4
      Your Employer / Business information
    = job.label :adress
    = job.text_field :address

    = job.label :contact, "Phone number"
    = job.text_field :contact
    = job.label :address2
    = job.text_field :address2

    = job.label :city
    = job.text_field :city

    = job.label :state
    = job.select :state, options_for_select(states)

    = job.label :zipcode
    = job.text_field :zipcode
  = submit_tag "Join Bold Networking"

users_controller.rb

class UsersController < ApplicationController

  def new
    @business_categories = BusinessCategory.all
    @user = User.new
    respond_to do |format|
      format.html
      format.json { render :json => @business_categories }
    end
  end

  def create
    @user_creation = CreateUser.new(params).run!
    if @user_creation
      redirect_to root_path
    else
      render :new
      #flash error message with errors

    end
  end

end

It's because @user is nil when you render :new. Even though you render :new, it doesn't call the new method that runs @user = User.new. You don't really want that anyway, or the form wouldn't keep any of the submitted values.

  def create
    @user_creation = CreateUser.new(params).run!
    if @user_creation
      redirect_to root_path
    else
      render :new
      @user = @user_creation.user
    end
  end

Notably in the above example, there is no user method on CreateUser objects—you'll have to create that.

If think this is getting complicated, then you'll understand why I initially warned about complexity, and asked whether you thought it would be worth it. 😄 (though maybe it is‽)

on render :new
@user_creation is equal to false