rails 创建父记录后创建关联记录（一对一关系）

tl; dr has-one-association-reference-when-are-objects-saved

原理

感谢大佬的解决方案

贴一段 rails guides 的讲解

When are Objects Saved?

When you assign an object to a has_one association, that object is automatically saved (in order to update its foreign key). In addition, any object being replaced is also automatically saved, because its foreign key will change too.

If either of these saves fails due to validation errors, then the assignment statement returns falseand the assignment itself is cancelled.

If the parent object (the one declaring the has_one association) is unsaved (that is, new_record?returns true) then the child objects are not saved. They will automatically when the parent object is saved.

If you want to assign an object to a has_one association without saving the object, use the build_association method.

例子

class User < ApplicationRecord
  has_one :wallet, dependent: :destroy # 一个【用户】对于一个【钱包】

  before_create :create_default_wallet

  def create_default_wallet
    build_wallet # 相当于 new 了一个【钱包】
    true
  end

  # 【用户】创建成功后，对应的【钱包】才 save
end

参考文献

has-one-association-reference-when-are-objects-saved

Rails - Best-Practice: How to create dependent has_one relations