Newbie question: Mapping Collections

Hi,

Day 3 with rails here. Forgive me. If this has been covered many times
before, pls just point me at the article.

I worked through the Rolling with Rails tutorial
(http://www.onlamp.com/pub/a/onlamp/2005/01/20/rails.html) built up my
cookbook. Things work great.

I now want to add Ingredients to my app. So, a Recipe will have 1 or
more Ingredients and any single ingredient can be referenced (belong
to?) any recipe.

How do I set up this relationship? With other languages I would create a
mapping table in my database which had two columns, a Recipe index and
Ingredient index. I could then write some simple SQL to pull all the
Ingredients for my Recipe or to get all the Recipes containing a
specific Ingredient. It doesn’t look like this is how it happens in
rails.

Do I modify my Ingredient class to have a ‘belongs_to_many’ relationship
to Recipe and Recipe to have a ‘has_many’ relationship to Ingredients?
How is this mapping done on the DB? What fields in the tables do I need
to add? Am I able to easily query the stuff mentioned above?

Thanks in advance,

Noah

On 7/6/06, Noah K. [email protected] wrote:

I worked through the Rolling with Rails tutorial (

How do I set up this relationship? With other languages I would create a
mapping table in my database which had two columns, a Recipe index and
Ingredient index. I could then write some simple SQL to pull all the
Ingredients for my Recipe or to get all the Recipes containing a specific
Ingredient. It doesn’t look like this is how it happens in rails.

You can use this approach with has_and_belongs_to_many
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#M000533

Alternativley you can use has_many :through
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#M000530

Josh S.'s blog has some good information on has_many :through and
has_and_belongs_to_many
http://blog.hasmanythrough.com/

Do I modify my Ingredient class to have a ‘belongs_to_many’ relationship
to

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