Question

I’m trying to create a form_for using the following fields. However, some of the fields correspond to one model, the RecipeIngredient class (model), whereas the bottom fields correspond to the Recipe class (model).

  <%= form_for(:recipe_and_ingredients, :url => {:action => 'create'}) do |f| %>

<!-- RecipeIngredient classs -->
<table>
<tr>
 <td>4</td>
 <td><%= f.text_field(:quantity) %></td>
 <td><%= f.text_field(:weight) %></td>
 <td><%= f.text_field(:units) %></td>
</tr>
</table> 


<!-- Recipe class -->
<table summary="Recipe form fields">
  <tr>
    <th>Recipe Name</th>
    <td><%= f.text_field(:recipe_name) %></td>
    <th>Total Grams</th>
    <td><%= f.text_field(:total_grams) %></td>
  </tr>
</table>

<div class="form-buttons">
  <%= submit_tag("Create Recipe") %>
</div>

<% end %>

However, in my controller:

 # Instantiate a new object using form parameters
  @recipe = Recipe.new(params[:recipe_and_ingredients])
  @ingredient = RecipeIngredient.new(params[:recipe_and_ingredients])

I get this error when I submit the form

  unknown attribute: quantity

I know this is because the Recipe model/class/table/whatever does not have a quantity column; that is a column within RecipeIngredient (which is supposed to be a join table between Recipe and some other table if that is relevant). When I submit the params however, how do I differentiate, in the code, which parameters belong to which class?

Answer 1

use
In the model: accepts_nested_attributes_for
In the controller: Nothing
In the routes: Nothing
In the view, at the point where you want the ‘nested’ fields, use f.fields_for :other_model do |inner| and then you can use inner.inner_field_name. I think inner would be ingredient in your case, if that is what RecipieIngredient is and you renamed it to ingredient. If receipieIngredient is actually a more complex join table redo as needed.

See more at http://railscasts.com/episodes/196-nested-model-form-part-1

I would name the entities ‘recipies’ and ‘ingredients’ and then have a form for a recipie that has fields_for :ingredients do |i|.

If you want Ingredient has_many recipies and Recipie has_many ingredients, you can do that too with has_many_through in both of the models pointing to a join model IngredientRecipie which belongs to_both recipie and ingredient but that doesn’t affect the form. Those relationships are used to retrieve data.

Note that if you have these has_many through you can use simple_form to just maintain the relationship with checkboxes for the relationships and no other code to write other than saving the data with one save.

Update:

Recipie (model)
Recipie has_many :recipie_ingredients
Recipie has many :ingredients, :through => :recipie_ingredients

Ingredient (model)
Recipie has_many :recipie_ingredients
Recipie has many :ingredients, :through => :recipie_ingredients

RecipieIngredient (model)
belongs_to :recipies
belongs_to :ingredients