Associations in seed.rb

Question

I have following models in my app

class Building < ApplicationRecord

  has_many :rooms, dependent: :destroy
  ...

class Room < ApplicationRecord

  belongs_to :building
  has_many :lessons, dependent: :destroy
  ...

class Lesson < ApplicationRecord

  belongs_to :room
  belongs_to :teacher
  belongs_to :course
  ...

Everything worked fine between Bulding and its rooms with this code:

if Building.find_by_code("PAR").nil?
   building = Building.create!({title: "Areál Parukářka", code: "PAR"})
    
   par_rooms.each do |room|
      building.rooms << Room.create({title: room[0], code: room[1]})
   end 
end 

Now I want to add lessons to each Room. With the following code, no error is raised, and when I add some "puts" it says that the lessons has been created, but they are not available inside the controller/view. Here's the seed I use:

if Building.find_by_code("PAR").nil?
  building = Building.create!({title: "Areál Parukářka", code: "PAR"})

  par_rooms.each do |room|
    new_room = Room.create({title: room[0], code: room[1]})
    building.rooms << new_room
    lesson = Lesson.create({start_at: DateTime.new(2018, 11, 20, 8), end_at: DateTime.new(2018, 11, 20, 9, 30), duration: 45, room_id: new_room.id, teacher_id: nil, course_id: nil})
    new_room.lessons << lesson
  end

rooms and lessons tables has the following schema:

create_table "rooms", force: :cascade do |t|
    t.string "title"
    t.string "code"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.integer "building_id"
    t.index ["building_id"], name: "index_rooms_on_building_id"
  end


create_table "lessons", force: :cascade do |t|
    t.datetime "start_at"
    t.datetime "end_at"
    t.integer "duration"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.integer "room_id"
    t.integer "teacher_id"
    t.integer "course_id"
    t.index ["course_id"], name: "index_lessons_on_course_id"
    t.index ["room_id"], name: "index_lessons_on_room_id"
    t.index ["teacher_id"], name: "index_lessons_on_teacher_id"
  end

Answer 1

lesson = Lesson.create({
    start_at: DateTime.new(2018, 11, 20, 8), 
    end_at: DateTime.new(2018, 11, 20, 9, 30), 
    duration: 45, room_id: new_room.id, 
    teacher_id: nil,     # is problematic with your model
    course_id: nil})     # is problematic with your model

Your model suggests that all relations are needed.

You should, if there are empty relations given, mark

belongs_to :teacher, optional: true

as optional.

Not that this solves your problem, but it should be the right direction.

For more ideas you should provide the schemas for teacher, course, room and building.