Hello,
I'm pretty new to Ruby on Rails (ROR) so I'm sorry if this is a silly thing to ask. I have tried looking at several tutorials online but most of them are for the earlier version of ROR and even the API is not helping me too much!
Basically I would like to create a drop down list in a form. I have simplified my problem so that you'll be able to understand it in a few lines.
A simple diagram is here: http://learningspirit.co.uk/class_diagram.png
The migration and model files are here: ## db/migrate/003_books.rb class Books < ActiveRecord::Migration def self.up create_table :books do |t| t.column :title, :string, :limit => 32, :null => false t.column :price, :float t.column :subject_id, :integer t.column :description, :text t.column :created_at, :timestamp end end
def self.down drop_table :books end end
## db/migrate/004_subjects.rb class Subjects < ActiveRecord::Migration def self.up create_table :subjects do |t| t.column :name, :string end
Subject.create :name => "Physics" Subject.create :name => "Mathematics" Subject.create :name => "Chemistry" Subject.create :name => "Psychology" Subject.create :name => "Geography" end
def self.down drop_table :subjects end end
## app/model/book.rb class Book < ActiveRecord::Base belongs_to :subject validates_presence_of :title validates_numericality_of :price, :message=>"Error message" end
## app/model/subject.rb class Subject < ActiveRecord::Base has_many :books end
The relevant book_controller.rb methods are: def new @book = Book.new @subjects = Subject.find(:all) end
def create @book = Book.new(params[:book]) if @book.save redirect_to :action => 'list' else @subjects = Subject.find(:all) render :action => 'new' end end
The problem I have is in the view for the form to create a new book entry. The view (app/views/book/new.html.erb) is looking like this at the moment:
<h1>Add new book</h1> <% form_for :book, @book, :url => { :action => "create" } do |f| %> <p> <label>Title</label>: <%= text_field @book, :title %> </p> <p> <label>Price</label>: <%= text_field @book, :price %> </p> <p> <label>Subject</label>: <%= collection_select :book, :subject_id, @subjects, :id, :name %> </p> <p> <label>Description</label>: <%= text_area @book, :description %> </p> <p> <%= f.submit "Create"%> </p> <% end %> <%= link_to 'Back', {:action => 'list'} %>
My problem is that I cannot get the drop down list to work! I have tried select (instead of collection_sort) but I am always getting errors. At the moment I have the following error:
undefined method `subject_id' for #<Book id: nil, created_at: nil, updated_at: nil>
I don't understand this at all because from the documentation, there should be a method there!
Please could some help me? What exactly are the arguments for the collection_select method? What is wrong with my collection_select call?
Thank you very much and I hope this wasn't too long winded! Inuka.
