Rails Formtastic nested form - form for attributes from join model

Question

The problem I am facing with Formtastic is that I have a Form to create a new Order. In this form I want to select multiple existing Food items from a list. These should be added to the new Order I am submitting. At the same time I also want to set attributes in the FoodOrder join model. This Model has an integer quantity attribute for which i would like to have a field in my form.

What I am basically looking for is a form that lists all Food Items and puts a field for the quantity on the same line as the Food Item it belongs to.

The Models

class Order < ActiveRecord::Base
  belongs_to :user
  belongs_to :restaurant
  has_many :food_orders
  has_many :foods, :through => :food_orders
end

class FoodOrder < ActiveRecord::Base
  belongs_to :food
  belongs_to :order
end

class Food < ActiveRecord::Base
  has_many :food_orders
  has_many :orders, :through => :food_orders
  belongs_to :category
end

This is one of the versions of the form I have tried so far. But I am just baffled and do not know how to get fields for the FoodOrder Model.

<%= semantic_form_for [@restaurant, @order] do |f| %>
  <%= f.inputs do %>
    <%= f.input :comment %><br />
    <%= f.input :table_id %><br />
    <%# <%= f.input :foods, :as => :check_boxes %>
    <%= f.inputs :for => :foods do |food| %>
      <%= food %>
      <%= food.inputs :quantity %>
    <% end %>
  <% end %>
  <%= f.buttons do %>
    <%= f.commit_button %>
  <% end %>
<% end %>

My models have these attributes

create_table "food_orders", :force => true do |t|
  t.integer  "quantity",   :null => false
  t.decimal  "price",      :null => false
  t.integer  "food_id",    :null => false
  t.integer  "order_id",   :null => false
  t.text     "comment"
  t.datetime "created_at", :null => false
  t.datetime "updated_at", :null => false
end

create_table "foods", :force => true do |t|
  t.integer  "category_id",                     :null => false
  t.string   "name",                            :null => false
  t.string   "description"
  t.string   "image"
  t.decimal  "default_price",                   :null => false
  t.boolean  "active",        :default => true, :null => false
  t.datetime "created_at",                      :null => false
  t.datetime "updated_at",                      :null => false
end

create_table "orders", :force => true do |t|
  t.integer  "restaurant_id",                    :null => false
  t.integer  "user_id",                          :null => false
  t.integer  "table_id",                         :null => false
  t.decimal  "total",                            :null => false
  t.datetime "finished_at"
  t.datetime "created_at",                       :null => false
  t.datetime "updated_at",                       :null => false
end

Answer 1

Basically what I would end up doing is creating a FoodOrder object for each Food then only save the ones that have a value above 0.

You could do that in a reject_if for the accepts_nested_attributes_for but that wouldn't deleted the old FoodOrders that someone might change from 3 to 0. So instead you will have to override the quantity= method for FoodOrder.

I've never used formtastic before but I'm going to take a guess and say that this should work.

<%= semantic_form_for [@restaurant, @order] do |f| %>
  <%= f.inputs do %>
    <%= f.input :comment %><br />
    <%= f.input :table_id %><br />
    <% @foods.each do |food|
      <%= f.semantic_fields_for :food_orders, 
                            @order.food_orders.detect_or_build_by_food(food)
                            do |food_order| %>
        <%= food %>
        <%= food_order.inputs :quantity %>
      <% end %>
    <% end %>
  <% end %>
  <%= f.buttons do %>
    <%= f.commit_button %>
  <% end %>
<% end %>

order.rb:

class Order < ActiveRecord::Base
  belongs_to :user
  belongs_to :restaurant
  has_many :foods, :through => :food_orders
  has_many :food_orders do
    def detect_or_build_by_food(food)
      record = self.detect{ |food_order| food_order.food_id == food.id }
      if record.nil?
        record = self.build(:food => food)
      end
      record
    end
  end

  accepts_nested_attributes_for :food_orders
end

food_order.rb:

class FoodOrder < ActiveRecord::Base
  belongs_to :food
  belongs_to :order

  def quantity=(quantity)
    if quantity <= 0
      self.destroy
    else
      self[:quantity] = quantity
    end
  end
end

I would hope that works but it is untested code, so yeah... Good Luck!