Rails - May 2009 - 2.3 Nested Model Forms; build new without updating existing

I''m trying to build something similar to a Facebook messaging app, in
which the view displays all the messages for a particular thread, with
a form box for replying at the bottom of the thread.

The problem is that using fields_for generates form fields for each
existing record, and for one new record. In this case, there is no
need to edit existing messages - just a need to add new messages.

Does anybody know how to do this? Code is below.

Models:
class MessageThread < ActiveRecord::Base
  has_many :messages
  accepts_nested_attributes_for :messages, :allow_destroy => true
end

class Message < ActiveRecord::Base
  belongs_to :message_threads
end

View (show.html.erb)

  <% @message_thread.messages.each do |message| %>
  <%= message.message %>
  <% end %>

<% form_for @message_thread do |thread_form| -%>
  <% thread_form.fields_for :messages do |message| %>
  <%= message.label :message %>
  <%= message.text_field :message %>
  <% end %>

  <%= submit_tag ''Send Message'' %>
  <% end -%>

Thanks.

I just wanted to follow up with my simple (maybe obvious) solution....
> <% form_for @message_thread do |thread_form| -%>
>   <% thread_form.fields_for :messages do |message| %>
        <% if message.object.new_record? %> # The
magic!
>        <%= message.label :message %>
>        <%= message.text_field :message %>
       <% end %>
>    <% end %>
Duh! If there''s a smarter way, I''m still listening.

On May 12, 4:43 am, Guitaronin
<arianr...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I''m trying to build something similar to a Facebook messaging app,
in
> which the view displays all the messages for a particular thread, with
> a form box for replying at the bottom of the thread.
>
> The problem is that using fields_for generates form fields for each
> existing record, and for one new record. In this case, there is no
> need to edit existing messages - just a need to add new messages.
>
> Does anybody know how to do this? Code is below.
>
> Models:
> class MessageThread < ActiveRecord::Base
>   has_many :messages
>   accepts_nested_attributes_for :messages, :allow_destroy => true
> end
>
> class Message < ActiveRecord::Base
>   belongs_to :message_threads
> end
>
> View (show.html.erb)
>
>   <% @message_thread.messages.each do |message| %>
>   <%= message.message %>
>   <% end %>
>
> <% form_for @message_thread do |thread_form| -%>
>   <% thread_form.fields_for :messages do |message| %>
>   <%= message.label :message %>
>   <%= message.text_field :message %>
>   <% end %>
>
>   <%= submit_tag ''Send Message'' %>
>   <% end -%>
>
> Thanks.

Hi,

On May 12, 9:43 am, Guitaronin
<arianr...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> The problem is that using fields_for generates form fields for each
> existing record, and for one new record.
The ''new record'' is behaviour I''m unaware of! I think
that you have to
build the new record in the association.
> Does anybody know how to do this? Code is below.
>
> Models:
> class MessageThread < ActiveRecord::Base
>   has_many :messages
>   accepts_nested_attributes_for :messages, :allow_destroy => true
> end
>
> class Message < ActiveRecord::Base
>   belongs_to :message_threads
> end
>
> View (show.html.erb)
>
>   <% @message_thread.messages.each do |message| %>
>   <%= message.message %>
>   <% end %>
>
> <% form_for @message_thread do |thread_form| -%>
>   <% thread_form.fields_for :messages do |message| %>
>   <%= message.label :message %>
>   <%= message.text_field :message %>
>   <% end %>
Nested attributes fields_for supports setting an explicit object as
the second parameter, like so:
<% thread_form.fields_for(:messages, Message.new) do |message| %>

Although the proper way would be to set @new_message or similar in the
controller and pass that, or thread_form.object.messages.build().

Hope that helps,
Andrew