Question

I have a typical elementary problems which I cannot find a nice solution for. Let’s take the typical many to many relationship in Rails, with the join table used to assign a value:

Recipe
    has_many :recipe_ingredients
    has_many :ingredients, :through => :recipe_ingredients
    accepts_nested_attributes_for :recipe_ingredients

Ingredient
    has_many :recipe_ingredients
    has_many :recipes, :through => :recipe_ingredients

RecipeIngredient
    belongs_to :recipe
    belongs_to :ingredient
    attr_accessible :quantity

Nothing strange here. Let’s say now I want to to create a new recipe with new ingredients all in one go. I have some JSON sent to the server like this:

{"recipe"=>
    {"name"=>"New Recipe", 
     "ingredients"=>
        [{"name" => "new Ingr 1", "quantity"=>0.1},
         {"name" => "new Ingr 2", "quantity"=>0.7}]
    }
}

I reckon I can navigate the params and create the objects one by one but I was looking into leveraging the many-to-many association and above all the accepts_nested_attributes_for, thus being able to do something like Recipe.create(params[:recipe]) and have the object tree created for me. If that means changing the JSON being sent, it is not a problem. 🙂

Answer 1

The JSON key should be "ingredients_attributes":

Recipe
  has_many :recipe_ingredients
  has_many :ingredients, :through => :recipe_ingredients
  attr_accessible :ingredients
  accepts_nested_attributes_for :ingredients # note this

and

{"recipe"=>
  {"name"=>"New Recipe", 
    "ingredients_attributes"=>
      [{"name" => "new Ingr 1", "quantity"=>0.1},
       {"name" => "new Ingr 2", "quantity"=>0.7}]
  }
}