Active Record DB Modeling - Ruby on Rails - mysql

Question

Ok guys, this might be a little bit confusing so stick with me. Let me start by introducing my tables. Basically I created four tables upon migration.
Students
Teachers
Subjects
Admin User
Here are my migration files:
Students:
def up
create_table :students, :id => false do |t|
t.integer "student_id",:primary_key => true
t.string "first_name", :limit => 25
t.string "last_name", :limit => 50
t.string "email", :default => ' ', :null => false
t.string "birthday"
t.string "subjects"
t.string "teachers"
t.string "username", :limit => 25
t.string "password_digest"
t.timestamps
end
Teachers:
def up
create_table :teachers, :id => false do |t|
t.integer "teacher_id", :primary_key => true
t.string "first_name"
t.string "last_name"
t.string "email", :default => ' ', :null => false
t.string "birthday"
t.string "subjects"
t.string "username", :limit => 25
t.string "password_digest"
t.timestamps
end
Subjects:
def up
create_table :subjects, :id => false do |t|
t.integer "subject_id", :primary_key => true
t.string "subject_name"
t.timestamps
end
end
Admin Users:
def up
create_table :admin_users, :id => false do |t|
t.integer "admin_user_id", :primary_key => true
t.string "username", :limit => 25
t.string "password_digest"
t.timestamps
end
end
So now let me get through the explanation. Basically:
one student can have many teachers
one teacher can have many students
one student can have many subjects
one teacher can teach many subjects
the admin can access all of this (create, edit, delete)
I created this fields and set them up on my models like this:
class Student < ApplicationRecord
has_and_belongs_to_many :subjects
has_and_belongs_to_many :teachers
has_many :admin_users
has_secure_password
self.primary_key = :student_id
end
class Teacher < ApplicationRecord
has_and_belongs_to_many :subjects
has_and_belongs_to_many :students
has_many :admin_users
has_secure_password
end
class Subject < ApplicationRecord
has_and_belongs_to_many :students
has_and_belongs_to_many :teachers
has_many :admin_users
# scope :search, lambda { |query| where(["name LIKE ?", "%#{query}%"])}
end
class AdminUser < ApplicationRecord
has_secure_password
scope :newest_first, lambda { order("created_at ASC") }
scope :oldest_first, lambda { order("created_at DESC") }
# scope :search, lambda { |query| where(["name LIKE ?", "%#{query}%"])}
end
Now I manually inserted data on mysql data record and then tried to pull up the records for student's subjects and teachers form fields.
How can I manage my database effectively esp teachers, students, and subjects??? Is there anything I need to do first to correlate the tables I have? Please help. Sorry for the long post. I am a newbie here. Appreciate your explanation (layman's term) and answers.
Check my models. Do I need to create a separate table to correlate teachers, students, and subjects?
Side Note: When I pull up my students and teachers field it gives me an error ActiveRecord_Associations_CollectionProxy:0x007f9c504361d0 ERROR.

Answer 1

I think this relation should work in your case:
Students:
def up
create_table :students, :id => false do |t|
t.integer "student_id",:primary_key => true
t.string "first_name", :limit => 25
t.string "last_name", :limit => 50
t.string "email", :default => ' ', :null => false
t.string "birthday"
t.string "subjects"
t.string "username", :limit => 25
t.string "password_digest"
t.timestamps
end
end
Ref: Generating auto increment with sequence 1001
Teachers:
def up
create_table :teachers, :id => false do |t|
t.integer "teacher_id", :primary_key => true
t.string "first_name"
t.string "last_name"
t.string "email", :default => ' ', :null => false
t.string "birthday"
t.string "subjects"
t.string "username", :limit => 25
t.string "password_digest"
t.timestamps
end
end
Subjects:
def up
create_table :subjects, :id => false do |t|
t.integer "subject_id", :primary_key => true
t.string "subject_name"
t.timestamps
end
end
Enrolled Subjects:
def up
create_table :enrolled_subjects, :id => false do |t|
t.integer "subject_id"
t.integer "teacher_id"
t.integer "student_id"
end
end
Model:
class Student < ApplicationRecord
has_many :enrolled_subjects
has_many :subjects, through: :enrolled_subjects
has_many :teachers, through: :enrolled_subjects
def teacher_names
self.teachers.map(&:first_name).join(", ")
end
end
class Teacher < ApplicationRecord
has_many :enrolled_subjects
has_many :subjects, through: :enrolled_subjects
has_many :students, through: :enrolled_subjects
end
class Subject < ApplicationRecord
has_many :enrolled_subjects
has_many :students, through: :enrolled_subjects
has_many :teachers, through: :enrolled_subjects
end
class EnrolledSubject < ActiveRecord::Base
belongs_to :student, foreign_key: :student_id
belongs_to :subject, foreign_key: :subject_id
belongs_to :teacher, foreign_key: :teacher_id
end
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