Rails: has_many through association, and the form for creating new instances

Question

I'm still super new with Rails, and just trying to get my first has_many through association set up.

Recipes have many ingredients, and each ingredient has an amount needed for the recipe. The ingredient_amount table has a recipe_id, an ingredient_id, and an amount.

When creating a new recipe, I want to be able to create these recipe/ingredient associations in the same place. In the end, I'm going to build an AJAX autocompleter for the ingredients. For now, as a baby step, I'd like to just assume the ingredient exists, and take care of checking once I've got this part down.

So, how can I make new.html.erb for recipes do this? How can I extend the form for more than one ingredient?

As it stands now, after going through http://weblog.rubyonrails.org/2009/1/26/nested-model-forms I still can't get any fields to add ingredients. The current code is below.

class Recipe < ActiveRecord::Base
    has_many :ingredient_amounts
    has_many :ingredients, :through => :ingredient_amounts
    accepts_nested_attributes_for :ingredient_amounts, :allow_destroy => true
end

class IngredientAmount < ActiveRecord::Base
  belongs_to :ingredient
  belongs_to :recipe
end

class Ingredient < ActiveRecord::Base
  has_many :ingredient_amounts
  has_many :recipes :through => :ingredient_amounts
end

Here's new.html.erb as I have it currently:

   <h1>New recipe</h1>

<% form_for @recipe do |f| %>
  <%= f.error_messages %>

  <p>
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </p>
  <p>
    <%= f.label :instructions %><br />
    <%= f.text_area :instructions %>
  </p>
  <p>
    <%= f.label :numberOfServings %><br />
    <%= f.text_field :numberOfServings %>
  </p>
  <p>
    <%= f.label :prepTime %><br />
    <%= f.text_field :prepTime %>
  </p>

  <p>
    <% f.fields_for :ingredient_amounts do |ingredient_form| %>
    <%= ingredient_form.label :ingredient_formedient_id, 'Ingredient' %>
      <%= ingredient_form.collection_select :ingredient_id, Ingredient.all, :id, :name, :prompt => "Select an Ingredient"%>
      <%= ingredient_form.text_field :amount %>
    <% unless ingredient_form.object.new_record? %>
        <%= ingredient_form.label :_delete, 'Remove:' %>
        <%= ingredient_form.check_box :_delete %>

    <% end %>
  </p>
  <% end %>
  <p>
    <%= f.submit 'Create' %>
  </p>
<% end %>

<%= link_to 'Back', recipes_path %>

The important bits of the recipe controller:

def new
    @recipe = Recipe.new

    respond_to do |format|
      format.html # new.html.erb
      format.xml  { render :xml => @recipe }
    end
  end
  def create
    @recipe = Recipe.new(params[:recipe])

    respond_to do |format|
      if @recipe.save
        flash[:notice] = 'Recipe was successfully created.'
        format.html { redirect_to(@recipe) }
        format.xml  { render :xml => @recipe, :status => :created, :location => @recipe }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @recipe.errors, :status => :unprocessable_entity }
      end
    end
  end

And... I have no idea where to start in the ingredient_amounts controller. This was my very first stab, and I'm pretty sure it's not so close :)

def new
    @recipe = Recipe.find(params[:recipe_id])
    @ingredient = Ingredient.find(params[:ingredient_id])
    @ingredient_amount = Recipe.ingredient_amounts.build
  end

Thanks for the help!

did you ever figure this out? i'm trying to do something almost identical. — Eric

firecall firecall · Accepted Answer · 2010-01-11T23:14:32

I believe what you are looking for is 'Nested Model Forms'.

Try this link: http://weblog.rubyonrails.org/2009/1/26/nested-model-forms

It's hard to know what to search for when you dont really know the terminology to begin with :)

Rails: has_many through association, and the form for creating new instances

1 Answers