Uninitialized constant error using a relationship

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