problem with a join table having additional data

Hi,

I am a very new to both Rails and SQL, and am trying to learn both by using an already established nutrition database. I am stuck on a join table that is a couple layers deep, and I was hoping that someone could help me out.

First, the purpose of the database is to map a food type (ground beef) to a list of nutrients (protein, fat, etc..).

Because I am working with a non-rails db, I have to set primary/ foreign keys myself.

The database has the following tables:

food_description   NDB_No (primary key)   NameOfFood # i.e. butter, chicken, ground beef, etc...

And it maps the food to a list of nutrients (i.e. protein, fat, carbs) through a nutrient_datas table:

nutrient_datas   NDB_No (primary key) # maps to the Food description   Nutr_No # maps to the name of the nutrient   Nutr_Val # how much of that nutrient this food has (24g of (Nutr_No)

Now, each of the nutrient_datas entries can have one or more sources. Just to make it real, let’s say:

Food Description: Ground Beef Nutrient Datas:   12 g of Protein      => Source 1: Cattleman’s Association     => Source 2: Beef, it's what's for dinner   10 g of Fat      => Source 1: PETA     => Source 2: Cardiologists of America

So, the Sources are handled by two more tables:

data_sources   DataSrc_ID (primary_key)   Title   Author

and a join table:

data_sources_nutrient_datas   NDB_No # maps to the food description (i.e. beef)   Nutr_No # maps to the Nutrient (i.e. Protein)   DataSrc_ID # maps to the Source (i.e. Cattlemans Association)

Here is my attempt to define three (kind of working) ActiveRecords

class NutrientData < ActiveRecord::Base   set_primary_key "NDB_No"   belongs_to :food_description, :foreign_key => "NDB_No"   belongs_to :nutrient_definition, :foreign_key => "Nutr_No"   belongs_to :source_code, :foreign_key => "Src_Cd"   has_many :data_sources_nutrient_datas, :foreign_key => "NDB_No"   has_many :data_sources, :through => :data_sources_nutrient_datas, :foreign_key => "NDB_No" end

class DataSource < ActiveRecord::Base   set_primary_key "DataSrc_ID"   has_many :data_sources_nutrient_datas, :foreign_key => "NDB_No"   has_many :nutrient_datas, :through => :data_sources_nutrient_datas, :foreign_key => "NDB_No" end

class DataSourcesNutrientData < ActiveRecord::Base   belongs_to :nutrient_data, :foreign_key => "NDB_No"   belongs_to :data_source, :foreign_key => "DataSrc_ID" end

I can say:   >> FoodDescription.find("03104").nutrient_datas[10].data_sources and be returned an array of sources for ALL of the nutrients (not just the 10th one).

So, my questions are:

1. Are my ActiveRecords OK (I think I am missing something)

2. How do I get FoodDescription.find("03104").nutrient_datas [10].data_sources to return only the records for nutrient (array) 10? (i.e. I need to select the data_source not just on the NDB_No, but also on the Nutr_No). Only the join table seems to have the Nutr_No info that I need, not the data_sources.

3. It seems best, of course, to query all of the data_sources at once, and then display only what is needed in the view. How can I do just that (a different (better) approach than above)?

Thanks in advance for your help!