Rails app using STI -- easiest way to pull these records?

Question

I'm learning my way around Rails and am working on a sample app to keep track of beer recipes.

I have a model called Recipe which holds the recipe name and efficiency.

I have a model called Ingredient which is using STI - this is subclassed into Malt, Hop, and Yeast.

Finally, to link the recipes and ingredients, I am using a join table called rec_items which holds the recipe_id, ingredient_id, and info particular to that recipe/ingredient combo, such as amount and boil time.

Everything seems to be working well - I can find all my malts by using Malt.all, and all ingredients by using Ingredient.all. I can find a recipe's ingredients using @recipe.ingredients, etc...

However, I'm working on my recipe's show view now, and am confused as to the best way to accomplish the below:

I want to display the recipe name and associated info, and then list the ingredients, but separated by ingredient type. So, if I have a Black IPA @ 85% efficiency and it has 5 malts and 3 hops varieties, the output would be similar to:

BLACK IPA (85%)
Ingredient List
MALTS:
malt 1
malt 2
...
HOPS:
hop 1
...

Now, I can pull @recipe.rec_items and iterate through them, testing each rec_item.ingredient for type == "Malt", then do the same for the hops, but that doesn't seem very Rails-y nor efficient. So what is the best way to do this? I can use @recipe.ingredients.all to pull all the ingredients, but can't use @recipe.malts.all or @recipe.hops.all to pull just those types.

Is there a different syntax I should be using? Should I using @recipe.ingredient.find_by_type("Malt")? Doing this in the controller and passing the collection to the view, or doing it right in the view? Do I need to specify the has_many relationship in my Hop and Malt models as well?

I can get it working the way I want using conditional statements or find_by_type, but my emphasis is on doing this "the Rails way" with as little DB overhead as possible.

Thanks for the help!

Current bare-bones code:

Recipe.rb

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

Ingredient.rb

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

Malt.rb

class Malt < Ingredient
end

Hop.rb

class Hop < Ingredient
end

RecItem.rb

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

recipes_controller.rb

class RecipesController < ApplicationController
  def show
    @recipe = Recipe.find(params[:id])
  end

  def index
    @recipes = Recipe.all
  end
end

Updated to add

I'm now unable to access the join table attributes, so I posted a new question:

Rails - using group_by and has_many :through and trying to access join table attributes

If anyone can help with that, I'd appreciate it!!

JofoCodin JofoCodin · Accepted Answer · 2011-08-25T15:21:29

It's been a while since I've used STI, having been burned a time or two. So I may be skipping over some STI-fu that would make this easier. That said...

There are many ways of doing this. First, you could make a scope for each of malt, hops, and yeast.

class Ingredient < ActiveRecord::Base
  has_many :rec_items
  has_many :recipes, :through => :rec_items
  named_scope :malt, :conditions =>  {:type => 'Malt'}
  named_scope :hops, :conditions => {:type => 'Hops'}
  ...
end

This will allow you to do something line:

malts = @recipe.ingredients.malt
hops = @recipe.ingedients.hops

While this is convenient, it isn't the most efficient thing to do, database-wise. We'd have to do three queries to get all three types.

So if we're not talking a ton of ingredients per recipe, it'll probably be better to just pull in all @recipe.ingredients, then group them with something like:

ingredients = @recipe.ingredients.group_by(&:type)

This will perform one query and then group them into a hash in ruby memory. The hash will be keyed off of type and look something like:

{"Malt" => [first_malt, second_malt],
 "Hops" => [first_hops],
 "Yeast" => [etc]
}

You can then refer to that collection to display the items however you wish.

ingredients["Malt"].each {|malt| malt.foo }

Rails app using STI -- easiest way to pull these records?

3 Answers