How do I get my create action to work for both a nested & non-nested resource?

Question

So I have two models Topic, Client. A Client has_and_belongs_to_many :topics, and a Topic has_and_belongs_to_many :clients.

Basically, what I want to happen is...when someone goes to my Topic#index, depending on how they got there (i.e. either via client/:id/topics or just /topics), I want the behavior of the create & new to be different. i.e. at /topics, it just creates a topic. At client/:id/topics it creates a topic and assigns it to that client.

My routes look like this:

  resources :topics
  resources :clients do
    resources :topics
  end

My Topics Controller looks like this:

  def new
        if params[:client_id]
            @client = Client.find(params[:client_id])
            @topic = @client.topics.build
        else
            @topic = Topic.new
        end

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

  def create
        if params[:client_id]
            @client = Client.find(params[:client_id])
            @topic = @client.topics.build(params[:topic])
        else
        @topic = Topic.new(params[:topic])
        end

    respond_to do |format|
      if @topic.save
        format.html { redirect_to @topic, notice: 'Topic was successfully created.' }
        format.json { render json: @topic, status: :created, location: @topic }
      else
        format.html { render action: "new" }
        format.json { render json: @topic.errors, status: :unprocessable_entity }
      end
    end
  end

My views/topics/_form.html.erb looks like this:

<%= form_for([@client, @topic]) do |f| %>
...
<% end %>

However, when I perform an action from client/:id/topics this is what the logs look like:

Started GET "/clients/1/topics/new" for 127.0.0.1 at 2012-09-10 14:33:06 -0500
Processing by TopicsController#new as HTML
  Parameters: {"client_id"=>"1"}
  Client Load (0.2ms)  SELECT "clients".* FROM "clients" WHERE "clients"."id" = ? LIMIT 1  [["id", "1"]]
  Rendered topics/_form.html.erb (3.6ms)
  Rendered topics/new.html.erb within layouts/application (4.7ms)
  User Load (0.3ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
   (0.2ms)  SELECT COUNT(*) FROM "roles" INNER JOIN "users_roles" ON "roles"."id" = "users_roles"."role_id" WHERE "users_roles"."user_id" = 1 AND (((roles.name = 'admin') AND (roles.resource_type IS NULL) AND (roles.resource_id IS NULL)))
  Rendered layouts/_navigation.html.erb (7.2ms)
  Rendered layouts/_messages.html.erb (0.1ms)
Completed 200 OK in 61ms (Views: 57.0ms | ActiveRecord: 0.7ms)

That looks good...everything seems to be in order here. But it is in the POST that things seem to be not working:

Started POST "/clients/1/topics" for 127.0.0.1 at 2012-09-10 14:33:13 -0500
Processing by TopicsController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"J172LuZQPv8=", "topic"=>{"name"=>"AMZN"}, "commit"=>"Create Topic", "client_id"=>"1"}
  Client Load (0.2ms)  SELECT "clients".* FROM "clients" WHERE "clients"."id" = ? LIMIT 1  [["id", "1"]]
   (0.1ms)  begin transaction
  SQL (186.2ms)  INSERT INTO "topics" ("created_at", "name", "updated_at") VALUES (?, ?, ?)  [["created_at", Mon, 10 Sep 2012 19:33:13 UTC +00:00], ["name", "AMZN"], ["updated_at", Mon, 10 Sep 2012 19:33:13 UTC +00:00]]
   (4.6ms)  commit transaction
Redirected to http://localhost:3000/topics/4
Completed 302 Found in 198ms (ActiveRecord: 191.1ms)

You will notice there is no assignment of the new topic to the client.

What am I missing?

Thanks!

Edit 1

Added puts debug statements to my create action, and this is the result I got after the POST action was executed - which indicates that is getting the params[:client_id] and not just params[:id]:

Served asset /application.js - 304 Not Modified (1ms)
**************************************************
This is the params[:client_id] => {3}
**************************************************
This is the params[:id] => {}


Started POST "/clients/3/topics" for 127.0.0.1 at 2012-09-10 15:06:31 -0500
Processing by TopicsController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"J172LuZQc5NYoiMSzDD3oY9vGmxxCX0OdxcGm4GSPv8=", "topic"=>{"name"=>"TEST2"}, "commit"=>"Create Topic", "client_id"=>"3"}
  Client Load (0.2ms)  SELECT "clients".* FROM "clients" WHERE "clients"."id" = ? LIMIT 1  [["id", "3"]]
   (0.1ms)  begin transaction
  SQL (0.7ms)  INSERT INTO "topics" ("created_at", "name", "updated_at") VALUES (?, ?, ?)  [["created_at", Mon, 10 Sep 2012 20:06:31 UTC +00:00], ["name", "TEST2"], ["updated_at", Mon, 10 Sep 2012 20:06:31 UTC +00:00]]
   (3.3ms)  commit transaction
Redirected to http://localhost:3000/topics/6
Completed 302 Found in 11ms (ActiveRecord: 4.3ms)

Edit 2:

So I tried something else that seems to work, but I would love to know why the above doesn't work.

If, in my Topic#create I just do this:

@client = Client.find(params[:client_id])
@topic = Topic.new(params[:topic])
@client.topics << @topic

It works fine.

But, again...I would love to know why the .build doesn't for HABTM or in this situation.

Answer 1

I think the issue is in the params[:client_id] it may be params[:id].

Can you put a puts statement in your if else block of create action, and then see which one is showing up when you hit the page(create a topic)

EDIT

You need to include accepts_nested_attributes_for in your model to support dynamic building of nested object attributes.

Refer this.

Answer 2

It seems I have to explicitly call save after the build is done on my @client object.

Otherwise, ActiveRecord won't save the transaction and insert a new record in the join_table.