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:
-
Are my ActiveRecords OK (I think I am missing something)
-
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. -
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!