has_and_belongs_to_many OR self-joining association

[cberry1971]

I have a basic set up question for my nutrition application:

The application will have users who log in and receive MEAL prescriptions for the upcoming week. Tables can include:

User
Food
Recipe (perhaps Meal)

1. I can have a has_and_belongs_to_many relationship between "Food" and "Recipe". Many recipes comprised of many foods.

OR

2. I can use a self-joining association

class Meal < ActiveRecord::Base
has_many :foods, :class_name => "Meal",
:foreign_key => "recipe_id"
belongs_to :recipe, :class_name => "Meal"
end

Finally:
I must remember the "User"... any need to consider polymorphic associations? The "User" will be prescribed "Meals" or "Recipes" on a weekly basis.

Thanks in advance.

[Mittineague]

I can grasp the concept of a many to many relationship between user <=> food, but I'm confused about the relationship between "food" and "recipe/meal". Can you give some examples?

[cberry1971]

yes thank you:

User A (small person) eats Meal A comprising Foods A,B&C

User B (larger person) eats Meal B comprising Foods 2*(A,B&C)

pretty sure i need a has_and_belongs_to_many for

User <=> Meal
Meal <=> Food

Can I do this between two different tables, where Meal is used 2x?

eg. do I just use two different join tables??? and away I go?