Active Record Associations undefined method 'val' (build,create enabled by has_many,belongs_to)

Question

I am quite new to rails and I have a bit of trouble understanding associations. I want to make a fast forum(just the thread - post mechanism nothing else) . My models are generated by :

1. rails generate scaffold Forumthread title:string
2. rails generate scaffold Forumpost title:string content:text username:string

In my models I added the associations namely:

class Forumthread < ActiveRecord::Base
    has_many :forumposts, dependent: :destroy
end

class Forumpost < ActiveRecord::Base
    belongs_to :forumthread
end

On the show page of a thread I want to be able to make a forumpost for that thread . I am trying to do it like this : view: <%= notice %>

<p>
  <strong>Title:</strong>
  <%= @forumthread.title %>
</p>

<% form_for(@post) do |f| %>

<div class="field">
    <%= f.label :title %><br>
    <%= f.text_field :title %>
  </div>
  <div class="field">
    <%= f.label :content %><br>
    <%= f.text_area :content %>
  </div>
  <div class="field">
    <%= f.label :username %><br>
    <%= f.text_field :username %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>


<%= link_to 'Edit', edit_forumthread_path(@forumthread) %> |
<%= link_to 'Back', forumthreads_path %>

and controller:

def show
    @current_thread = Forumthread.find_by_id(params[:id])
    @post = @current_thread.forumposts.build
  end

I didn't get to the create part because it seems it doesn't work just typing @current_thread.forumposts.build to create an object. What am I missing ? I want @post to be an object of type forumpost so I can create with @current_thread.forumposts.create(forumposts_params);

At the moment I get the following error:

undefined method `val' for #<Arel::Nodes::BindParam:0x007fe5c0648770>

I will happily provide more data if it is requested! .

Answer 1

I remember reading about this error occuring when foreign_key is missing (https://github.com/rails/rails/commit/78bd18a90992e3da767cfe492f1bc5d63077da8a) and it looks like this might be your case, since you didn't included it when genereting scaffold for Forumpost. Do you have forumthread_id column in your database table for Forumposts? If you don't know what I'm talking about - go to db/schema.rb file and and check if you can see something like:

 create_table "forumsposts", force: true do |t|
    #some other fields
    t.integer  "forumthread_id", null: false
    #some other fields
 end

If not, you will have to generate and run one more migration adding this missing foreign_key to Forumspost. Read about it on http://guides.rubyonrails.org/association_basics.html#options-for-belongs-to-foreign-key :), run rails generate migration AddForumthreadIdToForumpost, put something like the code below in newly created migration file and run rake db:migrate:

class AddForumthreadIdToForumpost < ActiveRecord::Migration
  def change
    add_column :forumposts, :forumthread_id, :integer, null: false
    add_index :forumposts, :forumthread_id
  end
end