Extra attributes from join table in a has_many through

Question

I have a Recipe , Ingredient , and RecipeIngredient .

class Recipe
  has_many :recipe_ingredients
  has_many :ingredients, through: :recipe_ingredients
end

My RecipeIngredient has additional attributes like amount , unit , type , etc.

If I wanted from a recipe.ingredients to retrieve these extra attributes, how would I go about that in a way that ideally does not introduce N+1 queries or anything else that degrades performance?

Answer 1

Untested but you can get back to me

Your question is a little vague but I think this is what you are looking for:

recipe = Recipe.includes(:ingredients).find(1)

Of course you can replace the find(1) with all or whatever method you want to use.

Then when you select an attribute from one of the ingredients of a recipe, it won't generate another query since it will have already fetched it.

Reference:

http://apidock.com/rails/ActiveRecord/QueryMethods/includes

Answer 2

ingredients = recipe.ingredients.all
recipe_ingredients = recipe.recipe_ingredients.all

# only two queries. no queries beyond this point

ingredients.each do |ingredient|
  recipe_ingredient = recipe_ingredients.find {|it| it.ingredient_id == ingredient.id }
  recipe_ingredient.amount # etc
end

Something like that perhaps?