Ruby on Rails: undefined method `model_name' f

Question

I am trying to allow a user to enter a project into a database. One of the fields allows them to enter multiple technologies for that project.

Here is my project controller, new and create action.

def new
  @project = Project.new
  @all_technols = Technol.all
  @project_technol = @project.projecttechnols.build

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

def create
  @project = Project.new(params[:project])
  params[:technols][:id].each do |technol|
    if !technol.empty?
      @project.projecttechnols.build(:technol_id => technol)
    end
  end
end

Here is my new project view for the multi select technology dropdown.

<%= fields_for(@project_technol) do |ab| %>
  <div class="tech">
    <%= ab.label "All Tech" %><br/>
    <%= collection_select(:technols, :id, @all_technols, :id, :tech, {}, {:multiple => true} ) %>
  </div>
<% end %>

project.rb

class Project < ActiveRecord::Base
  attr_accessible :tech
  has_many :projecttechnols
  has_many :technols, :through => :projecttechnols
end

technol.rb

class Technol < ActiveRecord::Base
  attr_accessible :tech
  has_many :projecttechnols
  has_many :projects, :through => :projecttechnols
end

projecttechnol.rb

class Projecttechnol < ActiveRecord::Base
  attr_accessible :project_id, :technol_id
  belongs_to :technol
  belongs_to :project
end

At the moment, I have a page where the user can enter a new technology. But I want to move this option to the create new project page, where they can either select existing technologies, or enter a new one, or do both, and they would save with that project.

When I try to save a new project however, I am getting this error.

Showing /home/james/Desktop/webapp/app/views/projects/new.html.erb where line #233 raised:

    undefined method `model_name' for NilClass:Class

Extracted source (around line #233):

233: <%= fields_for(@project_technol) do |ab| %>
234: 
235: <div class="tech">
236: <%= ab.label "All Tech" %><br/>

I am new to rails and still learning so please remember when answering. Thanks in advance.

EDIT

after changing

@project.projecttechnols.build(:technol_id => technol)

to

@project_technol = @project.projecttechnols.build(:technol_id => technol)

I now get this error:

NoMethodError in Projects#create

undefined method `map' for nil:NilClass

Extracted source (around line #240):

237: <div class="tech">
238: <%= ab.label "All Tech" %><br/>
239: 
240: <%= collection_select(:technols, :id, @all_technols, :id, :tech, {}, {:multiple => true} ) %>
241: </div>
242: <% end %>

EDIT 2

@all_technols = Technol.all in the create action

I now get this error.

NoMethodError in Projects#show

Showing /home/james/Desktop/webapp/app/views/projects/show.html.erb where line #181 raised:

undefined method `technol' for #<Project:0xb36823c>
Extracted source (around line #181):

178: <h3>Related books</h3>
179: 
180: <ul>
181:   <% @project.technol.each do |technol| %>
182:     <li><%= technol.tech %> <%= link_to "Details", technol_path(technol) %></li>
183:   <% end %>
184: </ul>

Answer 1

Your create action is rendering the new view again. However, @project_technol is not defined within the create action. The fields_for method calls model_name method on the argument passed in (@project_technol), but since @project_technol = nil, it's throwing that error. To fix this, within your create action, change

@project.projecttechnols.build(:technol_id => technol)

to

@project_technol = @project.projecttechnols.build(:technol_id => technol)