ActiveRecord::AssociationTypeMismatch - Ruby on Rails

Question

I've been running with some issues with adding a new record on my students table. Basically I have 3 tables that are associated with each other: Students, Teachers, Enrolled Subjects and Subjects.

The main issue here is that the subjects table was declared :string on both students and teachers table upon migration but is asking for an array instead:

Class CreateStudents < ActiveRecord::Migration[5.0]

  def up
  create_table :students, :id => false do |t|
    t.integer "student_id", :auto_increment => true, :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

    class CreateTeachers < ActiveRecord::Migration[5.0]
      def up
      create_table :teachers, :id => false do |t|
          t.integer "teacher_id", :auto_increment => true, :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

class CreateSubjects < ActiveRecord::Migration[5.0]
  def up
    create_table :subjects, :id => false do |t|
       t.integer "subject_id", :auto_increment => true, :primary_key => true
       t.string "subject_name"
       t.timestamps
    end
  end

class CreateEnrolledSubjects < ActiveRecord::Migration[5.0]
  def up
    create_table :enrolled_subjects, :id => false do |t|
      t.integer "subject_id"
      t.integer "teacher_id"
      t.integer "student_id"
    end
  end

Below is my code when adding a record inside rails console:

new_studend = Student.create(:student_id => 1, :first_name => 'Karl', :last_name => 'Geek', :email => 'ss.norton@gmail.com', :birthday => '12/04/1995', :subjects => ["English"], :username => 'samnorton2', :password => 'Grace02112')  

I also tried:

new_student = Student.create(:student_id => 1, :first_name => 'Jos', :last_name => 'Norton', :email => 'ss.norton@gmail.com', :birthday => '12/05/1995', :subjects => 'English', :username => 'samnorton2', :password => 'Grace02112')

But I got an error both:

When I used string 'English':

NoMethodError: undefined method `each' for "English":String

When I used array: :subjects => ['English']

ActiveRecord::AssociationTypeMismatch: Subject(#70237743894000) expected, got String(#70237706174560)

I am not sure what's happening here. But it's taking time for me to resolve. For my models I simply put the ff codes:

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(&:name).join(", ")
  end

  has_many :admin_users
  has_secure_password
  self.primary_key = :student_id


  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

    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

    class EnrolledSubject < ApplicationRecord
      belongs_to :student
      belongs_to :subject
      belongs_to :teacher
    end

class Teacher < ApplicationRecord

  has_many :enrolled_subjects

  has_many :subjects, through: :enrolled_subjects
  has_many :students, through: :enrolled_subjects
  has_many :admin_users
  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

Any idea? Sorry I am new ROR. Hope someone can help me and explain in layman's term what's happening on this.

Answer 1

The subjects string column on teachers and students is conflicting with what rails gives you in a has_many association. You'll want to drop these columns.

def change
  remove_column :students, :subjects
  remove_column :teachers, :subjects
end