Rails/SQL no results show from Query - ruby-on-rails

Question

Versions: CENTOS7, mysql2('>= 0.3.13', '< 0.5'), rails('4.2.6')
index.html.erb
<% #sections.each do |section| %>
<tr>
<td><%= section.course_id %></td>
<td><%= section.term_id %></td>
<td><%= section.user_id %></td>
</tr>
<% end %>
sections controller
class SectionsController < ApplicationController
before_action :authenticate_account!, except: [:show]
def index
#sections = User.find_by_account_id(current_user).courses
end
def show
end
end
createSections migration
class CreateSections < ActiveRecord::Migration
def change
create_table :courses do |t|
t.integer :course_id
t.timestamps null: false
end
create_table :terms do |t|
t.integer :term_id
t.timestamps null: false
end
create_table :users do |t|
t.integer :user_id
t.timestamps null: false
end
create_table :sections do |t|
t.belongs_to :course, index: true
t.belongs_to :term, index: true
t.belongs_to :user, index: true
t.timestamps null: false
end
end
end
course.rb model
belongs_to :user
has_many :sections
has_many :terms, :through => :sections
term.rb model
belongs_to :user
has_many :sections
has_many :courses, :through => :sections
section.rb model
belongs_to :course
belongs_to :term
belongs_to :user
user.rb
has_many :sections
has_many :courses, :through => :sections
has_many :terms, :through => :sections
Expected result: List the current(logged in) user's courses/terms/ID
Current result: blank
This is my first time working with rails and SO, I tried changing the relationships a few times to see if anything would change but not sure how to approach this. I have tried using ActiveRecord:Associations as a reference. What do I need to do to make this work?

Answer 1

If you already have current_user then you can just call the related models directly.
#sections = User.find_by_account_id(current_user).courses
to
#sections = current_user.courses

Answer 2

The first thing to address is that you typically want separate migrations for each distinct thing that you're migrating. It's a convention that helps you keep fine-grained control over your changes, and it helps keep your migrations clean.
Sometimes, though, you actually want to have a "mass" migration. You have a mass-migration here. In the mass-migration circumstance, the migration name should reflect the combined purpose, so you'd want to name it something like CreateCoreTables; CreateSections is too narrow a name for creating multiple tables. You will also need to change the name of the migration file to be 2016XXXXXXXX_create_core_tables.rb, where XXXXXXXXX is left as the previous value.
Next, you'll want to correct your use of keys (the _id columns), as these are improperly declaring the association fields, which will cause the associations to not work (or work incorrectly).
Instead, you want something like this:
class CreateCoreTables < ActiveRecord::Migration
def change
create_table :courses do |t|
t.timestamps
end
create_table :terms do |t|
t.timestamps
end
create_table :users do |t|
t.timestamps
end
create_table :sections do |t|
t.integer :user_id, null: false
t.integer :term_id, null: false
t.integer :course_id, null: false
t.timestamps
end
end
end
It's difficult to tell what the actual intended relationships are from the code provided. It would be worth reading on Active Record Migrations to make sure that you understand what relationships you intend, and how to describe them. While you're working out the migrations, keep revisiting the model relationships, as well. These are the bedrock of the application, so you want to spend time getting them right.
Remember, for ActiveRecord relationships, these rules will guide you:
If a model owns another model, use has_many or has_one
In the owned model, use belongs_to
If a model needs access to another model (but doesn't own it), use a has_many, :through relationship
Models cannot have has_many or has_one relationships directly to each other; you need an intermediate table in that case with the requisite belongs_to for each of the other tables
Once you have the migrations and relationships worked out, you can move on to the query. You can use Rails Eager Loading to optimize the query to retrieve the associations at the same time. This will address your current functional needs, and prevent an N+1 query issue at the same time.
#sections = Section.joins(courses: :terms).where(user: current_user)
When you have retrieved #sections, you can do these types of actions to get the data that you want. The courses and terms members are collections, and you can interact with them as though they were arrays:
#sections.each do |section|
puts "Section: #{section.id}"
puts "Number of user sections: #{#sections.courses.length}"
section.courses.each do |course|
puts "Course: #{course.id}"
end
puts "Number of user terms: #{#sections.terms.length}"
#sections.terms do |term|
puts "Term: #{term.id}"
end
puts "User's email: #{#sections.user.email}"
end
Once you've mastered these, you've got the basics of Rails. Work on one model/controller at a time to keep from overcomplicating the work; you can always add on more once once component is working like you expect. Always make sure that you have your foundation working before you move onto new aspects of the app that will depend on it.
Also, remember to use the Rails guides. They're very helpful, so keep them on hand at all times while you're learning. SO is also a great resource, and make sure that you ask pointed questions, so that you can get direct answers.