Select statement in a form partial for an HABTM association - ruby-on-rails

Question

I have two models Client and Topic. Both of which have a HABTM association between them.
I am trying to add a select statement in my _form partial in my Client views, that allows the user to add a topic to a client (or edit that topic, etc.).
This is what my form partial looks like:
<%= form_for(#client) do |f| %>
<div class="field">
<%= f.label :topic %><br />
<%= f.select :topics, Topic.all.collect { |topic| [topic.name, topic.id] }, {:include_blank => 'None'} %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
The first error I got was this:
ActiveModel::MassAssignmentSecurity::Error in ClientsController#create
Can't mass-assign protected attributes: topics
So, in my Client model, I added this:
attr_accessible :email, :firm_id, :name, :phone, :topics
This is the error I now get:
NoMethodError in ClientsController#create
undefined method `each' for "1":String
The create action of my Clients controller is very standard:
def create
#client = Client.new(params[:client])
respond_to do |format|
if #client.save
format.html { redirect_to #client, notice: 'Client was successfully created.' }
format.json { render json: #client, status: :created, location: #client }
else
format.html { render action: "new" }
format.json { render json: #client.errors, status: :unprocessable_entity }
end
end
end
These are the params submitted (notice that topics is being passed - instead of topic_id but topic_id doesn't work either):
{"utf8"=>"✓",
"authenticity_token"=>"J172LuZQc5NYoiMSzDD3oY9vGmxxCX0OdxcGm4GSPv8=",
"client"=>{"name"=>"Jack Daniels",
"email"=>"jack.daniels#some-email.com",
"phone"=>"2345540098",
"firm_id"=>"2",
"topics"=>"1"},
"commit"=>"Create Client"}
How can I get a topic assigned to my client on the creation of the client with this select statement?
Thanks!

Answer 1

When setting a "Topic" attribute, Client expects an instance of a Topic class.
Since you are passing IDs, you need to change:
<%= f.select :topics, Topic.all.collect { |topic| [topic.name, topic.id] }, {:include_blank => 'None'} %>
to set topic_ids instead:
<%= f.select :topic_ids, Topic.all.collect { |topic| [topic.name, topic.id] }, {:include_blank => 'None'} %>
And, of course, in attr_accessible:
attr_accessible :email, :firm_id, :name, :phone, :topic_ids