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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.

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5
  • you have t.string "teachers" in student table. What you expect student.teachers to return? Commented Jan 27, 2017 at 14:39
  • Hi Pardeep Dhingra, I edited my question sorry. Got confused. Commented Jan 27, 2017 at 14:44
  • Check my models. Do I need to create a separate table to correlate teachers, students, and subjects? Commented Jan 27, 2017 at 14:46
  • First remove that teachers string from student table and you need to study has_many through relations. Commented Jan 27, 2017 at 14:47
  • Can you point out one by one in the answer so that I can follow through? Commented Jan 27, 2017 at 14:47

1 Answer 1

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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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20 Comments

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?
Also when I manually insert data from mysql will it automatically populate the teachers and subjects field when students enrolled?
Don't add data manually through mysql. Try rails console to add data instead.
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
yeah on rails console.
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