online_exam.rb

#controller
  def add_new_chapter
    @chapter=Chapter.new
    @user=current_user
    @subjects=[]
    @subject_final=[[]]
    count=0
    if @user.admin?
        @subjects=Subject.all(:select=>'id,name,batch_id')
        puts "#{@subjects}"
        @subjects.each do |t|
            @subjects_all=Batch.find(t.batch_id,:select=>'name')
            @subject_final[count]['id']=t.id.to_i
            @subject_final[count]['name']="#{@subject_all.name} #{t.name}"
            count+=1
        end
    elsif @user.employee
        @employee=Employee.find_by_employee_number(@user.username)
        @subjects=EmployeesSubject.find_by_employee_id(@employee.id,:select=>'subject_id')
        @subjects.each do |t|
            @subjects_all=Batch.find(t.subject_id,:select=>'name')
            @subject_final[count]['id']=t.id.to_i
            @subject_final[count]['name']="#{@subject_all.name} #{t.name}"
            count+=1
        end
    else

    end

    respond_to do |format|
        format.js { render :action =>'new_chapter' }
    end
#error
Batch Columns (0.6ms)   SHOW FIELDS FROM `batches`
  Batch Load (0.1ms)   SELECT name FROM `batches` WHERE (`batches`.`id` = 2) 

TypeError (can't convert String into Integer):
  app/controllers/online_exam_controller.rb:57:in `[]='
  app/controllers/online_exam_controller.rb:57:in `add_new_chapter'
  app/controllers/online_exam_controller.rb:55:in `each'
  app/controllers/online_exam_controller.rb:55:in `add_new_chapter'