Active Record DB Modeling - Ruby on Rails

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.

you have `t.string "teachers"` in student table. What you expect `student.teachers` to return? — Pardeep Dhingra, Jan 27 '17 at 14:39
Hi Pardeep Dhingra, I edited my question sorry. Got confused. — , Jan 27 '17 at 14:44
Check my models. Do I need to create a separate table to correlate teachers, students, and subjects? — , Jan 27 '17 at 14:46
First remove that `teachers` string from student table and you need to study has_many through relations. — Pardeep Dhingra, Jan 27 '17 at 14:47
Can you point out one by one in the answer so that I can follow through? — , Jan 27 '17 at 14:47

score 1 · Answer 1 · edited May 23 '17 at 11:45

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

Example Repository

edited May 23 '17 at 11:45

Community

1
1

answered Jan 27 '17 at 14:55

Pardeep Dhingra

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Can you explain more? can you also site Pardeep and edit my migration what fields is supposed to be there? Do I need to create a new table with studend_id, teachers_id, and subjects_id on that? – Jan 27 '17 at 14:58
Also when I manually insert data from mysql will it automatically populate the teachers and subjects field when students enrolled? – Jan 27 '17 at 14:59
Don't add data manually through mysql. Try rails console to add data instead. – Pardeep Dhingra Jan 27 '17 at 15:05
That shouldn't be a problem until you are adding relation data to in `EnrolledSubject`. I haven't tested this relation, please give it a shot and let me know if it works for you. I will add more explanation – Pardeep Dhingra Jan 27 '17 at 15:07
yeah on rails console. – Jan 27 '17 at 15:07
last question. when I call this on my views. can it be like this? ***<%@students.each do |student|%> <%= student.student_id %> <%= student.username %> <%= student.first_name %> <%= student.last_name %> <%= student.email %> <%= student.birthday %> <%= student.teachers %> <%= student.subjects %> <% end %>*** – Jan 27 '17 at 15:08
Didn't get you. Like what? – Pardeep Dhingra Jan 27 '17 at 15:10
Would that automaticall populate the data then? – Jan 27 '17 at 15:12
`<%= student.teachers %>` and `<%= student.subjects %>` will be array of objects. You can't directly display it. you can create any helper method to help with that. like i am adding one in student model. – Pardeep Dhingra Jan 27 '17 at 15:12
Is there a way I can display the contents in a formatted text form for teachers and students? – Jan 27 '17 at 15:13
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/134201/discussion-between-jim-carter-and-pardeep-dhingra). – Jan 27 '17 at 15:14
now you can use `<%= student.teachers_name %>` this will return you comma separated teachers name. – Pardeep Dhingra Jan 27 '17 at 15:17
How about my admin user? am I going to just stick with my current migrations and models? (admin user is for the administrator) – Jan 27 '17 at 15:18
We don't need to link `admin_users` with any table above. You can directly call All `students` and its related `subjects` and `teachers` as admin. – Pardeep Dhingra Jan 27 '17 at 15:20
I see. probably that would be on the access part. for now its good to know if it can pull it up. one moment. trying this out. – Jan 27 '17 at 15:22
BTW Pardeep do you know a way to make the auto increment value for all of my id to start on a specific number upon migration lets say the student id must start on the number 1001 and then incrementing...DO you know? – Jan 27 '17 at 15:24
I only used this *** t.integer "teacher_id", :auto_increment => true, :primary_key => true*** but i am not sure if we can put :default => 1001 – Jan 27 '17 at 15:25
would that work on MYSQL? isnt that not for PostgreSQL? – Jan 27 '17 at 15:42
I successfully migrated the files and tried to add a new record via rails console. **stud = Student.create(:student_id => 1, :first_name => 'Sam', :last_name => 'Norton', :email => 'samuelnico.norton@gmail.com', :birthday => '12/05/1990', :subjects => 'English', :username => 'samnorton05', :password => 'Grace0512')** BUT GOT THIS ERROR **ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :enrolled_subjects in model Student** – Jan 27 '17 at 15:44
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/134307/discussion-between-pardeep-dhingra-and-jim-carter). – Pardeep Dhingra Jan 29 '17 at 15:59

Active Record DB Modeling - Ruby on Rails

1 Answers1