get association values in rails forms

I'm building an app where a User has tasks and a task has a location. The tasks and locations are in a nested_form using formtastic_cocoon, which is the formtastic gem with a jQuery extension.

The location.address field is an autocomplete text field searching on addresses that already exist in the database. So when the user selects the address, a hidden location_id in the form is populated.

What I am trying to do is that when the user goes to edit the task, I want it to display the currently selected address, but I don't see anywhere that I can retrieve that value. I can get the location_id, as that is in the task model, but I can't seem to get the associated location.address.

the models are

class Task < ActiveRecord::Base
     attr_accessible :user_id, :date, :description, :location_id

     belongs_to :user
     has_one :location
end

class Location < ActiveRecord::Base
     attr_accessible :address, :city, :state, :zip

     has_many :tasks
end 

then in my form, I have

  <div class="nested-fields"> 
     <%= link_to_remove_association "remove task", f %>
      <div class="searchAddress">
         < input type="text" value="HERE IS WHERE I WANT TO SHOW THE ADDRESS" >
     </div>
   <%= f.hidden_field :location_id %>
   <%= f.inputs :date, description %>
</div>

----------- edited to include all formtastic code ---------------

form.html.erb
<%= semantic_form_for @user, :html=>{:multipart=true} do |form| %>

    <%= form.inputs :username, :photo %开发者_JS百科>


      <%= form.semantic_fields_for :tasks do |builder | %>

   <%= render 'task_fields', :f => builder %>
  <% end %>
<% end %>

------- end edit -------------- I have tried outputing different manner of 'f', but don't see any reference to the associated locations, yet if I debug User.Task[0].Location outside of the form, I get the correct location details. How do I get that inside the form??

--------- update ------------

getting a bit closer on this. It turns out I can output

<%= debug f.object %>

I get the task object returned. Unfortunately it does not include the location object, just the value of the location_id field.

Did you try @task.location.address ?

Your approach is right. But there is some slide miss-conception declaring association. I'ld like to change as below:

# app/models/task.rb

class Task < ActiveRecord::Base
  attr_accessible :user_id, :location_id, :date, :description

  belongs_to :user
  belongs_to :location
end

As we are storing location foreign key in the tasks table, it's better to declare belongs_to association here.

# app/models/location.rb

class Location < ActiveRecord::Base
  attr_accessible :address, :city, :state, :zip

  has_many :tasks

  # this method will return full address of a location
  def full_address
    [address, city, state, zip].reject(&:blank?).join(", ")
  end
end 

Then you need to add the full_address of a selected location.

# app/views/users/_task_fields.html.erb

<div class="nested-fields"> 
  <%= link_to_remove_association "remove task", f %>
  
  <div class="searchAddress">
    <input type="text" value="<%= f.object.location&.full_address %>">
  </div>
  
  <%= f.hidden_field :location_id %>
  <%= f.inputs :date, description %>
</div>