undefined method `model_name' for NilClass:Class - Rails application - ruby-on-rails

Question

So I have seen other articles here on stack about this and a lot of the time people are not doing #post = post.new. I read some where to use the plural...??
any ways I am getting this error on my discussion code:
Model
class Discussion < ActiveRecord::Base
has_many :comment
belongs_to :author
attr_accessible :author_id, :content, :title
validate :comment, :presence => true
validate :title, :presence => true
end
Discussion Controller
class DiscussionsController < ApplicationController
def index
#discussion = Discussion.new
#discussions = Discussion.all
end
def create
#discussion = Discussion.create(params[:discussion])
if #discussion.save
redirect_to tasks_path, :flash => {:success => 'Created a new discussion'}
else
redirect_to tasks_path, :flash => {:error => 'Failed to create a discussion'}
end
end
end
Discussion Form
<%= form_for #discussion do |f| %>
<p><%= f.label :title %>
<%= f.text_field :title %></p>
<p><%= f.label :content %>
<%= f.text_area :content %></p>
<% end %>
Discussion Routes
resources :discussions do
resources :comments
end
Now as far as I know I am doing this right, because I have a task form set up essentially the same way - but I have looked at my code for hours and have googled and tried other examples and now i see this:
undefined method `model_name' for NilClass:Class
Extracted source (around line #1):
1: <%= form_for #discussion do |f| %>
2:
3: <p><%= f.label :title %>
4: <%= f.text_field :title %></p>
Which should mean that I am missing something from my controller.....is it as asilly as a spelling mistake? >.>

Answer 1

Have you tried putting this in your discussion controller?
def new
#discussion = Discussion.new
end

Answer 2

I believe your problem is that you are trying to create a discussion on a task form but have only defined the discussion controller and not the task controller.

Answer 3

u have to add :method => :post to the form for creating the object else the form will get submitted with GET request.
<%= form_for #discussion , :method => :post do |f| %>

Answer 4

Is that the index view that has the form_for?
If not, then you should add a new action to the controller and do #discussion = Discussion.new there and not in your index action.

Answer 5

if ur model relationships are exactly as u have provided, then they are incorrect
class Discussion < ActiveRecord::Base
has_many :comment #has_many :comments
belongs_to :author
attr_accessible :author_id, :content, :title
validate :comment, :presence => true #valide :comments, :presence => true
validate :title, :presence => true
end