Rails 3 Nested Models unknown attribute Error

Question

• I have a model \"Issue\" and a nested Model \"Relationship\"

• In the issue.rb I have mentioned:

  has_many :relationships, :dependent => :d         
  
  
          

Answer 1

Here is the working skeleton code: I created a new project and tried the combination of the other answers, and finally made it to work.

Here is my solution, after that are the things to watch out for. I am using different models so bear with me:

• My models are: discussion has_many posts.
• Discussion has no attributes.
• Posts has content:text and discussion_id:integer.

Working Code

(model) discussion.rb

has_many :posts
accepts_nested_attributes_for :posts

(model) post.rb

belongs_to :discussion

routes.rb

resources :discussions do
  resources :posts
end

(discussion view) _form.html.erb

<%= form_for(@discussion) do |f| %>
  <%= f.fields_for :posts, @post do |p| %>
    <%= p.text_area :content %>
  <% end %>
  <%= f.submit %>
<% end %>

(controller) discussions_controller.rb

  def new
    @discussion = Discussion.new
    @post = @discussion.posts.build

    respond_to do |format|
      format.html # new.html.erb
      format.xml  { render :xml => @discussion }
    end
  end

  def create
    @discussion = Discussion.new(params[:discussion])

    respond_to do |format|
      if @discussion.save
        format.html { redirect_to(@discussion, :notice => 'Discussion was successfully created.') }
        format.xml  { render :xml => @discussion, :status => :created, :location => @discussion }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @discussion.errors, :status => :unprocessable_entity }
      end
    end
  end

---

Possible things that can go wrong

First, Thilo was right, I get unknown attribute: post if I do

# WRONG!
f.fields_for :post

Second, I have to have the @post instance variable in new action otherwise the post.context textarea will not show up.

# REQUIRED!
@post = @discussion.posts.build

Third, If I use the f.fields_for @post, the create action will complain unknown attribute: post too.

# WRONG!
f.fields_for @post do |p|

Use this instead:

# RIGHT!
f.fields_for :posts, @post  do |p|

---

The End

So yeah, I wish we get to see more documentations on this (can't see any useful ones). For example I see some use of form_for [@discussion, @post] but I can never get it to work.