Use RAKE Task to move CSV to POSTGRES relational DB - ruby-on-rails

Question

I have the following models.
class Lesson < ActiveRecord::Base
has_many :books
has_many :vocabularies
has_many :sentenses
end
class Book < ActiveRecord::Base
belongs_to :lesson
end
class Vocabulary < ActiveRecord::Base
belongs_to :lesson
end
class Sentense < ActiveRecord::Base
belongs_to :lesson
end
With the following table schema:
Table Lesson [lesson_number, lesson_name]
Table Books [lesson_id, page_start, page_finish]
Table Vocabulary [lesson_id, word, meaning]
Table Sentences [lesson_id, sentence, sentence meaning]
And I have a CSV file with 15,000 lessons. The CSV file uses the same structure of 2 books, 10 vocabulary, 2 sentences consistently throughout all lesson plans.
My thoughts are to start like this.
namespace :import_csv do
desc "IMPORT Lessons"
task :lessons => :environment do
CSV.foreach('CcyTbl.csv') do |row|
lesson_name_id = row[0]
lesson_name = row[1]
Lesson.create(lesson_name_id: lesson_name_id, lesson_name: lesson_name)
end
end
desc "IMPORT BOOKS"
task :books => :environment do
CSV.foreach('CcyTbl.csv') do |row|
lesson_name_id = row[0]
book_name = row[3]
book_start_pg = row[7]
book_end_pg = row[8]
Lesson.create(lesson_name_id: lesson_name_id, book_name: book_name, book_end_pg: book_end_pg)
end
end
That much seems straight forward but I am struggling with:
How to handle null values.
Some lessons have two books
(Think column 3 has book1 and book2 is column 9 and sometimes book2 is null)
Lessons might have 5-10 vocabulary words
(Column 10 vocabulary 1, column 11 vocabulary 1 meaning, column 12 vocabulary, etc)
What is the best way to import the data in this CSV into their respective tables? Does it make more sense to create multiple rake tasks to do each portion or can it be done in one go?
UPDATE
Here is a link to a sample of the header row and first row of data.
(It is a bit too long to share a picture.)

Answer 1

You may want to create a data object that makes it easier to work with the CSV data. Decoupling the CSV format with the model creation will make the whole process simpler:
csv = CSV.new(body, headers: true, header_converters: :symbol, converters: :all)
data = csv.to_a.map {|row| row.to_hash }
See CSV reference.
Now we have an easy way to access each field.
data.each do |d|
lesson = Lesson.create!(d[:join], ...)
book = Book.create!(lesson: lesson, page_start:..)
end
BTW & FWIW,
class Sentense < ActiveRecord::Base
should be
class Sentence < ActiveRecord::Base