用抽象类在Rails中表示has_many关系

Question

我有一段关系，我很难建模。

我有一个Subscription类，它是一个常规的ActiveRecord模型，它可以有一个或多个PaymentSources。但问题是，付款来源可能会引用CreditCard或BankAccount。

鉴于这些模型与它们相关的数据非常不同，我觉得STI不是一个很好的选择。所以我想知道在Rails中是否存在已建立或推荐的方法，其中模型has_many是另一个模型，实际上是2个或更多类的抽象，它们不共享相同的数据布局。

理想情况下，在这个特定示例中，我可以说subscription.payment_source.default之类的内容，并将其引用CreditCard或BankAccount，具体取决于用户选择的首选结算方式

Answer 1

TLDR：

[更新]经过一番思考后，我会做选项2（更完整的解决方案），这是一个具有前瞻性的灵活性，但如果你不需要所有这些复杂性，我只做选项1。

选项1：

class Subscription < ApplicationRecord
  belongs_to :credit_card
  belongs_to :bank_account

  def payment_sources
    [credit_card, bank_account].compact
  end

  def default_payment_source
    case user.preferred_billing_method # assuming you have an integer column in users table called `preferred_billing_method`
    when 0 then credit_card # asssuming 0 means "Credit Card"
    when 1 then bank_account # assuming 1 means "Bank Account"
    else NotImplementedError
    end
  end
end

用法

Subscription.first.default_payment_source
# => returns either `CreditCard` or `BankAccount`, or `nil`

Subscription.first.payment_sources.first
# => returns either `CreditCard` or `BankAccount`, or `nil`

选项2：

class User < ApplicationRecord
  belongs_to :default_payment_source, class_name: 'PaymentSource'
  has_many :subscriptions
end

class Subscription < ApplicationRecord
  belongs_to :user
  has_many :payment_sources_subscriptions
  has_many :payment_sources, through: :payment_sources_subscriptions
end

# This is just a join-model
class PaymentSourcesSubscription < ApplicationRecord
  belongs_to :subscription
  belongs_to :payment_source

  validates :subscription, uniqueness: { scope: :payment_source }
end

# this is your "abstract" model for "payment sources"
class PaymentSource < ApplicationRecord
  belongs_to :payment_sourceable, polymorphic: true
  has_many :payment_sources_subscriptions
  has_many :subscriptions, through: :payment_sources_subscriptions

  validates :payment_sourceable, uniqueness: true
end

class CreditCard < ApplicationRecord
  has_one :payment_source, as: :payment_sourceable
end

class BankAccount < ApplicationRecord
  has_one :payment_source, as: :payment_sourceable
end

用法：

User.first.default_payment_source.payment_sourceable
# => returns either `CreditCard` or `BankAccount`, or `nil`

Subscription.first.payment_sources.first.payment_sourceable
# => returns either `CreditCard` or `BankAccount`, or `nil`