即使为空，也需要字段：true

Question

我正在尝试将一些种子数据添加到我的数据库中，但 ActiveRecord 不允许我创建没有关联用户的类别。

ActiveRecord::Schema.define(version: 2020_07_18_233635) do

  # These are extensions that must be enabled in order to support this database
  enable_extension "plpgsql"

  create_table "categories", force: :cascade do |t|
    t.string "name"
    t.bigint "user_id"
    t.string "image_url"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.index ["user_id"], name: "index_categories_on_user_id"
  end

  create_table "users", force: :cascade do |t|
    t.string "email", default: "", null: false
    t.string "encrypted_password", default: "", null: false
    t.string "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    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

  add_foreign_key "categories", "users"
  add_foreign_key "goals", "categories"
end

当我尝试创建类别时：

category = Category.create!({name: 'Fitness', image_url: 'some_url'})

我收到这个错误：

ActiveRecord::RecordInvalid (Validation failed: User must exist)

编辑：
这是我的 Category class:

class Category < ApplicationRecord
  belongs_to :user
  has_many :goals
end

Answer 1

在 Rails 5 之前，belongs_to 关联的默认设置是可选的。但是，对于 Rails >= 5，则相反；默认情况下会检查关联对象是否存在。在关联中指定 :optional 以选择退出：

class Category < ApplicationRecord
  belongs_to :user, optional: true
  has_many :goals
end

即使为空，也需要字段：true

Field required even though null: true

ruby

activerecord

ruby-on-rails

devise