NoMethodError - Ruby on Rails - ruby-on-rails

Question

I'm working through Code4Startup airbnb course (https://code4startup.com/projects/build-airbnb-with-ruby-on-rails-level-1) but I'm trying to adapt it for my own idea - an airbnb for education courses for my local colleges. I'm new to ruby and stackoverflow, I've tried searching for the solution for ages but my issue is that I don't know how to correctly describe it, so please explain it like I'm 5!
The error I'm receiving:
The error seems to be suggesting that my course model isn't being built correctly or that it is reverting back to the Listing model somehow (perhaps because my course_params aren't correct?)
NoMethodError in Courses#new
Showing /Users/Jack_R/code/rails/planet_study/app/views/courses/new.html.erb where line #22 raised:
undefined method `type' for #<Listing:0x007fc25da72ea8>
Extracted source (around line #22):
20
21
22
<div class="form-group">
<label>Course Type</label>
<%= f.select :type, [["English Language", "English Language"], ["Culture", "Culture"], ["Sports", "Sports"], ["Tech/Science", "Tech/Science"], ["Adventure", "Adventure"], ["Mixture", "Mixture"]],
id: "type", prompt: "Select...", class: "form-control" %>
</div>
</div>
My Models
I have a User model, a Listing model and a Course model (User>Listing>Course):
class User < ApplicationRecord
has_many :listings
has_many :courses, :through => :listings
end
Listing model:
class Listing < ApplicationRecord
belongs_to :user
has_many :courses
end
Course model:
class Course < ApplicationRecord
belongs_to :listing
end
Courses Controller
class CoursesController < ApplicationController
before_action :set_course, except: [:index, :new, :create]
before_action :authenticate_user!, except: [:show]
def index
#courses = current_user.listings.courses
end
def new
#course = current_user.listings.build
end
def create
#course = listings.build(course_params)
if #course.save
redirect_to listing_course_path(#course), notice: "Saved..."
else
render :new, notice: "Something went wrong..."
end
end
def show
def listing
end
def pricing
end
def description
end
def photo_upload
end
def amenities
end
def location
end
def update
if #course.update(course_params)
flash[:notice] = "Saved..."
else
flash[:notice] = "Something went wrong..."
end
redirect_back(fallback_location: request.referer)
end
private
def set_course
#course = Course.find(params[:id])
end
def room_params
params.require(:course).permit(:name, :type, :summary, :address, :places, :start_date, :finish_date, :price)
end
end
end
Course new.html.erb
<div class="panel panel-default">
<div class="panel-heading">
Create your course listing
</div>
<div class="panel-body">
<div class="devise-container">
<%= form_for #course do |f| %>
<div class="row">
</div>
<div class="col_md_4 select">
<div class="form-group">
<label>Course Type</label>
<%= f.select :type, [["English Language", "English Language"], ["Culture", "Culture"], ["Sports", "Sports"], ["Tech/Science", "Tech/Science"], ["Adventure", "Adventure"], ["Mixture", "Mixture"]],
id: "type", prompt: "Select...", class: "form-control" %>
</div>
</div>
<div class="col_md_4 select">
<div class="form-group">
<label>Places</label>
<%= f.select :places, [["1", 1], ["2", 2], ["3", 3], ["4", 4], ["5", 5], ["6", 6], ["7", 7]],
id: "places", prompt: "Select...", class: "form-control" %>
</div>
</div>
</div>
<div><%= f.submit "Create My Course", class: "btn btn-primary-green" %></div>
<% end %>
</div>
</div>
</div>

Answer 1

type is a reserved word in Rails. You can create a model with a type attribute, but you can't perform actions on this model until you rename the type attribute.
If you try to create a new record, through the rails console, you'll see a message like:
$ rails console
[1] pry(main)> Course.new(name: 'first', type: 'some type')
ActiveRecord::SubclassNotFound: The single-table inheritance mechanism
failed to locate the subclass: 'some type'. This error is raised because
the column 'type' is reserved for storing the class in case of
inheritance. Please rename this column if you didn't intend it to be
used for storing the inheritance class or overwrite
Course.inheritance_column to use another column for that information.
from
/Users/***/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/activerecord-5.1.4/lib/active_record/inheritance.rb:196:in
`rescue in find_sti_class'
As the message says, you must rename the type attribute to be able to work with it, to do it just run a migration to change this name and edit the file created, like:
$ rails generate migration rename_type_to_type_of
In the generated file use the rename_colum method, and specify first the model, then the old attribute name, and then the new one, like:
class RenameTypeToTypeOf < ActiveRecord::Migration[5.1]
def change
rename_column :courses, :type, :type_of
end
end
After that you can run rails db:migrate. Note type_of is just a poor suggestion of mine, you can adapt it as you want.