Rails complex view form with has_many :through association

Question

I'm trying to create a rails app for recipes, but am confused on how to create the view forms and controller logic. I have 2 models, Recipe and Item, joined in a has_many :through association with an Ingredient model as follows:

class Recipe < ActiveRecord::Base
    has_many :ingredients
    has_many :items, :through => :ingredients
end

class Item < ActiveRecord::Base
    has_many :ingredients
    has_many :recipes, :through => :ingredients
end

class Ingredient < ActiveRecord::Base
    # Has extra attribute :quantity
    belongs_to :recipe
    belongs_to :item
end

This association works in the console. For example:

Recipe.create( :name => 'Quick Salmon' )
Item.create( :name => 'salmon', :unit => 'cups' )
Ingredient.create( :recipe_id => 1, :item_id => 1, :quantity => 3)

Recipe.first.ingredients
=> [#<Ingredient id: 1, recipe_id: 1, item_id: 1, quantity: 3]

Recipe.first.items
=> [#<Item id: 1, name: "salmon", unit: "cups"]

However, I don't understand how to create the new recipe view so that I can add ingredients directly to a recipe in one page. Do I need to use fields_for or nested attributes? How do I build the view form and controller logic to create a recipe, with ingredients, in one page?

I'm on Rails 3.1.3.

Answer 1

The accepts_nested_attributes_for-method is what you are looking for. Ryan Bates has done an excellent Railscast on it.

You should also check the documentation for Active Record Nested Attributes