无法自动加载常量 Chart，需要 chart.rb 来定义它

Question

I'm getting a "Unable to autoload constant Chart, expected chart.rb to define it" error, but I do not where to start to find the problem. I have tried many things, but nothing seems to work. Any help will be very appreciated.

Chart model

class Chart < ApplicationRecord
    belongs_to :user, optional: true
end

In the code above, the:user is parent and connected to Chart.

Chart Controller

class ChartsController < ApplicationController
  before_action :set_chart, only: [:show, :edit, :update, :destroy]

  # GET /charts
  # GET /charts.json
  def index
    @charts = Chart.all
  end

  # GET /charts/1
  # GET /charts/1.json
  def show
    @chart = Chart.find(params[:id])
  end

  # GET /charts/new
  def new
    @chart = Chart.new
  end

  # GET /charts/1/edit
  def edit
  end

  # POST /charts
  # POST /charts.json
  def create
    @chart = Chart.new(chart_params)

    respond_to do |format|
      if @chart.save
        format.html { redirect_to @chart, notice: 'Chart was successfully created.' }
        format.json { render :show, status: :created, location: @chart }
      else
        format.html { render :new }
        format.json { render json: @chart.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /charts/1
  # PATCH/PUT /charts/1.json
  def update
    respond_to do |format|
      if @chart.update(chart_params)
        format.html { redirect_to @chart, notice: 'Chart was successfully updated.' }
        format.json { render :show, status: :ok, location: @chart }
      else
        format.html { render :edit }
        format.json { render json: @chart.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /charts/1
  # DELETE /charts/1.json
  def destroy
    @chart = Chart.find(params[:id])
    if @chart.present?
      @chart.destroy
    end
    respond_to do |format|
      format.html { redirect_back(fallback_location: '/charts')}
      format.json { head :no_content }
    end
  end

  private

    def chart_params
      params.require(:chart).permit(~~)
    end
end

The error says that there is a problem at line 22 which is

  # GET /charts/new

Answer 1

This error happens when the model is placed in a wrong directory. The path of the chart model should be

app/models/chart.rb

Move the chart model to the correct location, it will work fine.