Question

In the browser address bar i have http://localhost:3000/comment/index?post_id=6, i can access the post_id in the index,but when trying to create comment/post in the create action, it says couldnt find post without post ID in the log.What is going on here?thank you in advance.

Comments controller:

def index
  @post=Post.find(params[:post_id])
end

def create
  @post     = Post.find(params[:post_id])
  @comment  = @post.comments.build(params[:comment])
  @comment.save

  respond_with( @comment, :layout => !request.xhr? )          
end

comments/index view:

<%= form_for :comment, :remote => true,
                       :url => { :controller => "comments",
                                 :action     => "create"
                               },
                       :html => { :id => 'new-comment'} do |f|
%>
  <%= f.hidden_field :post_id, :value => @post.id %>
  <%= f.text_area :body %>
  <%= f.submit "post" %>
<% end %>

In the log:

Started POST "/comments" for 127.0.0.1 at 2011-10-17 14:06:36 -0700
  Processing by CommentsController#create as JS
  Parameters: {"utf8"=>"✓",  
    "authenticity_token"=>"cxQm2K2xwsyw0DY2XLNvkcMQI+wM96LpEENbfQqxu5c=",
    "comment"=> {"post_id"=>"6", "body"=>"This is the comment"},
    "commit"=>"post"}
  Completed 404 Not Found in 23ms

  ActiveRecord::RecordNotFound (Couldn't find Post without an ID):

Answer 1

If you take a look in the params hash in your log, you’ll see this:

{ "utf8"=>"✓",
  "authenticity_token"=>"cxQm2K2xwsyw0DY2XLNvkcMQI+wM96LpEENbfQqxu5c=",
  "comment"=> {
      "post_id"=>"6", # <-- there's your post_id
      "body"=>"This is the comment" },
  "commit"=>"post" }

So the post ID is there, but it’s inside the comment hash. So, in your create action, you just need to change to:

def create
  @post=Post.find(params[:comment][:post_id])
  @comment = @post.comments.build(params[:comment])
  @comment.save
  respond_with( @comment, :layout => !request.xhr? )          
end

However, you should be able to simplify the create action a bit.

def create
  @comment = Comment.new(params[:comment])
  @comment.save
  respond_with( @comment, :layout => !request.xhr? )
end

Since the post_id is in the comment params, the comment will automatically be associated with the post when you create it, without having to look up the record. If you need to access the post in your view, you can use @comment.post.