How can I display the name instead of an ID in rails - ruby-on-rails

Question

I am trying to have a drop down from the other model and display its name in the index page
I have a 3 tables "students", "classrooms", and "classroom_students"
what I am trying is when a student is created he should be able to add the classroom from a dropdown which is populated from classroom table, at the moment the drop down is working however it is getting the id from the dropdown
How to get the classroom name to display in index page
classroom model
class Classroom < ApplicationRecord
belongs_to :user
has_many :classroom_students
has_many :students, through: :classroom_students
end
student model
class Student < ApplicationRecord
has_many :classroom_students
has_many :classrooms, through: :classroom_students
validates :student_fname, presence: true, length: { minimum: 3, maximum: 50 }
end
classroom_student model
class ClassroomStudent < ApplicationRecord
belongs_to :classroom
belongs_to :student
end
students controller
def student_params
params.require(:student).permit(:student_fname, :student_lname, :gender, :dob, :aboriginal, :esl, :special_provisions, :user_id, :classroom_id, :group_id, :active)
end
classrooms controller
def classroom_params
params.require(:classroom).permit(:classroom_name, :classroom_year, :classroom_student)
end
students views form
<%= form.select :classroom_id, Classroom.where(:user_id => current_user.id).map {|r| [r.classroom_name, r.id]} %>
student index
at the moment it is id but I want it to be classroom name
<td><%= student.classroom_id %>
Schema file
create_table "classroom_students", force: :cascade do |t|
t.integer "classroom_id"
t.integer "student_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "classrooms", force: :cascade do |t|
t.string "classroom_name"
t.date "year"
t.string "classroom_student"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "users_id"
t.integer "user_id"
t.string "classroom_year"
t.index ["users_id"], name: "index_classrooms_on_users_id"
end
create_table "students", force: :cascade do |t|
t.string "student_fname"
t.string "student_lname"
t.boolean "gender"
t.string "dob"
t.boolean "aboriginal"
t.boolean "esl"
t.text "special_provisions"
t.integer "user_id"
t.integer "classroom_id"
t.integer "group_id"
t.boolean "active"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.string "classroom_name"
end

Answer 1

Your association says that student has many classrooms but your database schema says you have a clasroom_id too in the students table. Remove that classroom_id first if you need to associate a student to multiple classrooms. Then your select says:
<%= form.select :classroom_id, Classroom.where(:user_id => current_user.id).map {|r| [r.classroom_name, r.id]} %>
Now as you have multiple classrooms associated to one student so this will not work because classroom_id is not valid. Instead it should be like this:
<%= f.select :classroom_ids, Classroom.where(user_id: current_user.id).map { |r| [r.classroom_name, r.id] }, {}, multiple: true %>
This will associate multiple classrooms with the student.
And donot forget to add classroom_ids in strong params:
def student_params
params.require(:student).permit(:student_fname, :student_lname, :gender, :dob, :aboriginal, :esl, :special_provisions, :user_id, :classroom_id, :group_id, :active, :classroom_ids => [])
end
Hope this helps.

Answer 2

First of all, you have an association User has_many :classrooms, so you can't think that you only have 1 classroom.
You can get all the classes associated to an user with something like this:
<%= f.form_for #student do |f| %>
<%= f.collection_select(:classrrom_id, Classroom.all, :id, :classroom_name,
{:prompt => "Select your classrooms"}, {:multiple => true}) %>
<% end %>
And at your students_controller.rb you should add classroom_ids to your params
def student_params
params.require(:student).permit(:student_fname, :student_lname, :gender,
:dob, :aboriginal, :esl, :special_provisions, :user_id, :classroom_id,
:group_id, :active, :classroom_ids => [])
end