Associate Pre-existing Record with Pre-Existing Parent (2 parent objects)

Question

I have several models in nested attributes that I'm working with.

I have "teams" (has many constests), and "contests" (belongs to Team). But I also want contests to reference "categories" as a child object (a contest can only have one category, and a category can have may contests).

The way the logic works is that a team is created first, then a contest, and after that I want to be able to select from a list of categories (in a partial) and establish the association (set the category_id in contest to the id value in a category). It makes sense to me how this is done when creating a new contest as a child of team, but I am hitting my head agains the wall when it comes to creating the second relationship (existing contest to an existing parent category).

The controller that gives me the show view for a contest is:

def show
@team = Team.find(params[:team_id])
@contest = Contest.find(params[:id])
@categories = Category.all

respond_to do |format|
  format.html # show.html.erb
  format.json { render json: [@contest] }
end

end

In the show view I have this code:

<p><b>Name:</b><%= @contest.name %></p>
<%= link_to 'Edit', edit_team_contest_path(@team, @contest) %> |
<%= link_to 'Back', team_contests_path %>
<br />
<%= render 'categories/index'%>

And my partial _index for categories contains this code:

<table>
<% @categories.each do |category| %>
<tr>
<td><%= category.level1 %></td>
<td><%= category.level2 %></td>
<td><%= category.level3 %></td>
<td><%= category.level4 %></td>    
<td><%= link_to 'Show', category %></td>
<td><%= link_to 'Edit', edit_category_path(category) %></td>
<td><%= link_to 'Destroy', category, confirm: 'Are you sure?', method: :delete %></td>
<%end%>
</table>

Where I am so flummoxed is where to place the code (in the Contest or Category controller?) for setting the category-contest parent-child relationship, as well as which view (the Contest show view, or the Category _index partial?). I am pretty certain that I am not understanding something fundamental about Rails here, so if anyone could point me to the docs that might clear up my befuddlement I'd very much appreciate it.

Answer 1

Okay, here's how I ended up solving my problem (in case anyone finds it later and uses the same search terms I tried):

Models:

team.rb
 has_many :contests, :dependent => :destroy

category.rb
 has_many :contests

contest.rb
 belongs_to :team, :foreign_key => "team_id"
 belongs_to  :category, :class_name => 'Category', :foreign_key =>"category_id"
 accepts_nested_attributes_for :category

Controller:

contests_controller
def update
@contest = Contest.find(params[:id])
@team = @contest.team
if !params[:category_id].nil?
  @category = Category.find(params[:category_id]) 
  @contest.update_attributes(:category_id => @category.id)
end
respond_to do |format|
  if @contest.update_attributes(params[:contest])
   blah
  else
    blah
  end
end
end

Categories View (_index), a partial in the contests/show view, includes these three bits of code:

<table>
<% @categories.each do |category| %>
<tr>
<td><%= form_for [category, @contest] do |f| %>
    <% f.submit "Select" %>
    <% end %></td>
</tr>
<%end%>
</table>

And that is what it takes to associate a record that belong to another parent with another parent in a different model (after the first relationship has been created).