您好，当我尝试创建属于用户和Nounou的“孩子”时，我的应用程序Rails出现问题，但是我的问题是当我创建“孩子”时我是具有ID的用户，但是我还没有选择名词ou，所以我还没有名词no_id，这是我的不同代码（我尝试输入optional：true，但是不起作用： 模型和架构

class Enfant < ApplicationRecord
  belongs_to :user
  belongs_to :nounou,optional: true
end


class Nounou < ApplicationRecord
  has_many :enfants
end


class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable,:lockable,:timeoutable,:trackable and :omniauthable
  devise :database_authenticatable,:registerable,:recoverable,:rememberable,:validatable
  has_many :enfants
end


  create_table "enfants",force: :cascade do |t|
    t.string "last_name"
    t.string "first_name"
    t.bigint "nounou_id",null: false
    t.bigint "user_id",null: false
    t.datetime "created_at",precision: 6,null: false
    t.datetime "updated_at",null: false
    t.index ["nounou_id"],name: "index_enfants_on_nounou_id"
    t.index ["user_id"],name: "index_enfants_on_user_id"
  end

  create_table "nounous",force: :cascade do |t|
    t.string "name"
    t.integer "price"
    t.string "localisation"
    t.integer "evaluation"
    t.integer "places"
    t.string "first_name"
    t.string "last_name"
    t.string "photo"
    t.datetime "created_at",null: false
  end

  create_table "users",force: :cascade do |t|
    t.string "email",default: "",null: false
    t.string "encrypted_password",null: false
    t.string "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.datetime "created_at",null: false
    t.string "username"
    t.string "photo"
    t.string "first_name"
    t.string "last_name"
    t.index ["email"],name: "index_users_on_email",unique: true
    t.index ["reset_password_token"],name: "index_users_on_reset_password_token",unique: true
  end

end