Selectbox and values ruby

Question

I'm a bit new in ruby/rails/POO and I'm a bit lost in a form that I'm realizing. I'm using the gem formtastic and I'm doing it in haml.

I have this model

class Help < ActiveRecord::Base
  attr_accessible :answer, :category, :question

  validates :category, presence: true, uniqueness: true
  validates :question, presence: true
  validates :answer, presence: true
end

In my form, I want the possibility to create a new Question/Answer with its category. The category should be selected in a selectbox but if the category I want is not listed yet, I want to have the ability to add it.

Here's the form

 = semantic_form_for @help do |f|
  = f.inputs do
    = f.input :category, :as => :select, :collection => Help.category
    = f.input :category
    = f.input :question
    = f.input :answer

  = f.action :submit, :as => :button

EDIT :

class HelpsController < ApplicationController
  # GET /helps
  # GET /helps.json
  def index
    @helps = Help.all.sort_by {|f| f.category}

    respond_to do |format|
      format.html # index.html.erb
      format.json { render json: @helps }
    end
  end

  # GET /helps/1
  # GET /helps/1.json
  def show
    @help = Help.find(params[:id])

    respond_to do |format|
      format.html # show.html.erb
      format.json { render json: @help }
    end
  end

  # GET /helps/new
  # GET /helps/new.json
  def new
    @help = Help.new

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @help }
    end
  end

  # GET /helps/1/edit
  def edit
    @help = Help.find(params[:id])
  end

  # POST /helps
  # POST /helps.json
  def create
    @help = Help.new(params[:help])

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

  # PUT /helps/1
  # PUT /helps/1.json
  def update
    @help = Help.find(params[:id])

    respond_to do |format|
      if @help.update_attributes(params[:help])
        format.html { redirect_to @help, notice: 'Help was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: "edit" }
        format.json { render json: @help.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /helps/1
  # DELETE /helps/1.json
  def destroy
    @help = Help.find(params[:id])
    @help.destroy

    respond_to do |format|
      format.html { redirect_to helps_url }
      format.json { head :no_content }
    end
  end
end

When I try to reach /help/new it actually says to me :

undefined method `model_name' for NilClass:Class

The aim is to have in the selectbox, categories already registered, and if the user is not founding the category he wants to use in the selectbox, he can create one by typing it in the input.

Any clues to help me doing this ?

Cordially , Rob

Answer 1

I found a method that does half what i wanted. It's the method pluck. I defined a static method in my model :

 def self.getcat
    Help.pluck(:category)
 end

Then in my form in simply call this method on my collection :

= f.input :category, :as => :select, :collection => Help.getcat