How to Write a Simple Nested, has_many :through, many-to-many Form in Rails 3.1?

问题

I am building a recipe manager as a first rails app. I have a many-to-many, nested set of models based on this quite nice ERD. Ideally, I would like to create a form that allows me to create the recipe in a single form. Also, I would like the user to be able to write/paste the ingredients and steps into a single text field, respectively. In the code below, there is a virtual attribute that parses the cr separated lists in the form to attempt this.

I keep getting a "readonly" has_many through error when I write the ingredients. I understand that, based on excellent help I got offline, my join is not properly setup.

To simplify things, I would like to assign the ingredients list to either the first step or every step. How do I write the code so that it manually creates the join model with the virtual attribute?

My Four Models:

recipe.rb

    class Recipe < ActiveRecord::Base
      has_many :steps, :dependent => :destroy
      has_many :stepingreds, :through => :steps
      has_many :ingredients, :through => :stepingreds
      validates_presence_of :name, :description
      attr_writer :step_instructions, :ingredient_names
      after_save :assign_steps, :assign_ingredients

      def step_instructions
        @step_instruction || steps.map(&:instruction).join("\n")
      end

      def ingredient_names
        @ingredient_name || ingredients.map(&:name).join("\n")
      end

    private

    def assign_steps
        if @step_instructions
          self.steps = @step_instructions.split(/\n+/).map do |instruction|
            Step.find_or_create_by_instruction(instruction)
          end
        end
    end

      def assign_ingredients
        if @ingredient_names
          self.ingredients = @ingredient_names.split(/\n+/).map do |name|
            Ingredient.find_or_create_by_name(name)
          end
        end
      end
    end

step.rb

    class Step < ActiveRecord::Base
      #attr_accessible :recipe_id, :number, :instructions
      belongs_to :recipe
      has_many :stepingreds, :class_name => 'Stepingred'
      has_many :ingredients, :through => :stepingreds
    end

stepingred.rb

    class Stepingred < ActiveRecord::Base
      belongs_to :ingredient
      belongs_to :step, :class_name => 'Step'
    end

ingredient.rb

    class Ingredient < ActiveRecord::Base
      has_many :stepingreds
      has_many :steps, :through => :stepingred
      has_many :recipes, :through => :steps
    end

And here is my stripped down form:

    <%= form_for @recipe do |f| %>
      <%= f.error_messages %>
      <p>
        <%= f.label :name %><br />
        <%= f.text_field :name %>
      </p>
      <p>
        <%= f.label :description %><br />
        <%= f.text_area :description, :rows => 4 %>
        </p>
         <p>
        <%= f.label :ingredient_names, "Ingredients" %><br />
        <%= f.text_area :ingredient_names, :rows => 8 %>
      </p>
      <p>
        <%= f.label :step_instructions, "Instructions" %><br />
        <%= f.text_area :step_instructions, :rows => 8 %>
      </p>
      <p><%= f.submit %></p>
    <% end %>

My database schema:

    ActiveRecord::Schema.define(:version => 20110714095329) do
      create_table "ingredients", :force => true do |t|
        t.string   "name"
        t.datetime "created_at"
        t.datetime "updated_at"
      end
      create_table "recipes", :force => true do |t|
        t.string   "name"
        t.text     "description"
        t.datetime "created_at"
        t.datetime "updated_at"
      end
      create_table "stepingreds", :force => true do |t|
        t.integer  "recipe_id"
        t.integer  "step_id"
        t.integer  "ingredient_id"
        t.float    "amount"
        t.datetime "created_at"
        t.datetime "updated_at"
      end
      create_table "steps", :force => true do |t|
        t.integer  "recipe_id"
        t.integer  "number"
        t.text     "instruction"
        t.datetime "created_at"
        t.datetime "updated_at"
      end
    end

Please let me know if you have any suggestions or can recommend another piece of sample code I could model this app after.

回答1:

You need to add accepts_nested_attributes_for :ingredients, :stepingreds, :steps in Recipe.rb to be able to create the associated objects through a single @recipe object.

http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html

来源：https://stackoverflow.com/questions/6730345/how-to-write-a-simple-nested-has-many-through-many-to-many-form-in-rails-3-1