class GroupsController < ApplicationController

  def index
    @groups = Group.all
    @neighborhoods = Neighborhood.all
  end

  def show
    @group = Group.friendly.find(params[:id])
    @users = @group.users
    @neighborhood = Neighborhood.find(@group.neighborhood_id)
    @neighborhood_name = @neighborhood.name
  end

  def new
    if current_user
      @group = Group.new
      @neighborhoods = Neighborhood.all.map{|u| [ u.name, u.id ] }
    else
     redirect_to new_user_session_path, notice: 'You are not logged in.'
    end
  end


  # When User creates group, create a UserGroup with is_leader: true
  def create
    @group = Group.new(group_params)
    respond_to do |format|
      if @group.save
        user_group = UserGroup.new(user: current_user, group: @group)
        user_group.update(is_leader: true)
        user_group.save
        format.html { redirect_to @group, notice: "Group was successfully created." }
      else
        format.html { render :new }
      end
    end
  end


  def member_listing
    @group = Group.friendly.find(params[:id])
    user_ids = @group.user_groups.pluck(:user_id)
    @members = User.where(id: user_ids)
  end

  def group_params
    params.require(:group).permit(:name, :description, :neighborhood_id)
  end
end

class GroupsController < ApplicationController

  def index
    @groups = Group.all
    @neighborhoods = Neighborhood.all
  end

  def show
    @group = Group.friendly.find(params[:id])
    @users = @group.users
    @neighborhood = Neighborhood.find(@group.neighborhood_id)
    @neighborhood_name = @neighborhood.name
  end

  def new
    if current_user
      @group = Group.new
      @neighborhoods = Neighborhood.all.map{|u| [ u.name, u.id ] }
    else
     redirect_to new_user_session_path, notice: 'You are not logged in.'
    end
  end


  # When User creates group, create a UserGroup with is_leader: true
  def create
    @group = Group.new(group_params)
    respond_to do |format|
      if @group.save
        user_group = UserGroup.create(user: current_user, group: @group, is_leader: true)
        format.html { redirect_to @group, notice: "Group was successfully created." }
      else
        format.html { render :new }
      end
    end
  end


  def member_listing
    @group = Group.friendly.find(params[:id])
    user_ids = @group.user_groups.pluck(:user_id)
    @members = User.where(id: user_ids)
  end

  def group_params
    params.require(:group).permit(:name, :description, :neighborhood_id)
  end
end

Change new to create for user_group in create method
Change new to create for user_group in create method
