ruby-on-rails - Rails : set a model attribute as read-only, 但允许通过方法更新

Question

我有一个账户模型，我希望其中的balance 是只读的，但它可以通过私有(private)方法更新。

目前

class Account < ActiveRecord::Base
  def deposit(amount)
    # do some stuff and then
    update_balance(amount)
  end

  private

  def update_balance(amount)
    self.balance += amount
  end

end

但是，这仍然是可能的:

account = Account.first
account.balance += 5
account.save

我希望上面给出一个错误，但仍然能够做到:

account.balance #=> 0
account.deposit(5)
account.balance #=> 5

Answer 1

您可以为属性定义一个私有(private) setter :

class Account < ActiveRecord::Base

  private

  def balance=(the_balance)
    write_attribute(:balance, the_balance)
  end
end

然后，你不能在你的 Account 类之外调用它:

Account.new(balance: 1234)
# => ActiveRecord::UnknownAttributeError: unknown attribute 'balance' for 'Account'

Account.new.balance = 1234
# => NoMethodError: private method `balance=' called for <Account ...>