Uninitialized constant error using a relationship - ruby-on-rails

Question

I followed the instructions here to create a model Lesson in which there is a student and a teacher (both of the model User) and also a lesson start date.
#Lesson Controller
class Lesson < ActiveRecord::Base
belongs_to :student, class_name => 'User'
belongs_to :teacher, class_name => 'User'
end
#User Controller
class User < ActiveRecord::Base
has_many :lessons_to_attend, :class_name => 'Lesson', :foreign_key => 'student_id'
has_many :lessons_to_teach, :class_name => 'Lesson', :foreign_key => 'teacher_id'
end
The migration went smoothly and so on a page I try to query the student's lessons for tomorrow:
<% #date = 1.day.from_now %>
<%= #date.strftime("%A")%></br>
<%= #date.strftime("%-d/%-m/%y")%>
<% #user.lessons_to_attend.each do |l| %>
Lesson
<% end %>
But when I navigate to this page I get the error Uninitialized constant error Lesson::User
What did I miss out? I'll include the User controller in case something needs to be added in there.
class UsersController < ApplicationController
before_action :set_user, only: [:show, :edit, :update, :destroy]
# GET /users
# GET /users.json
def index
#users = User.all
end
# GET /users/1
# GET /users/1.json
def show
#user = User.find(params[:id])
end
# GET /users/new
def new
#user = User.new
end
# GET /users/1/edit
def edit
end
# POST /users
# POST /users.json
def create
#user = User.new(user_params)
respond_to do |format|
if #user.save
format.html { redirect_to #user, notice: 'User was successfully created.' }
format.json { render :show, status: :created, location: #user }
else
format.html { render :new }
format.json { render json: #user.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /users/1
# PATCH/PUT /users/1.json
def update
respond_to do |format|
if #user.update(user_params)
format.html { redirect_to #user, notice: 'User was successfully updated.' }
format.json { render :show, status: :ok, location: #user }
else
format.html { render :edit }
format.json { render json: #user.errors, status: :unprocessable_entity }
end
end
end
# DELETE /users/1
# DELETE /users/1.json
def destroy
#user.destroy
respond_to do |format|
format.html { redirect_to users_url, notice: 'User was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_user
#user = User.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def user_params
params[:user]
end
end

Answer 1

Two things:
belongs_to :student, class_name => 'User'
belongs_to :teacher, class_name => 'User'
Syntax error on class_name. That should either be :class_name => 'User' or class_name: 'User'.
The other thing is that I think you need to set your inverse_of on both sides of the association.
class Lesson < ActiveRecord::Base
belongs_to :student, class_name: 'User', inverse_of: :lessons_to_attend
belongs_to :teacher, class_name: 'User', inverse_of: :lessons_to_teach
end
class User < ActiveRecord::Base
has_many :lessons_to_attend, class_name: 'Lesson', foreign_key: 'student_id', inverse_of: :student
has_many :lessons_to_teach, class_name: 'Lesson', foreign_key: 'teacher_id', inverse_of: :teacher
end