条件语句辅助和重构 Rails

Question

我正在开发一个集成了比特币 API 的应用程序，我正在为条件语句而苦苦挣扎，我认为这是因为我对 ActiveRecord 或 SQL 方法缺乏了解。

这是期望的行为：

调用API并生成并保存一个比特币地址。
需要向用户显示相同的比特币地址，直到对其进行付款。
一旦付款完成并且用户想要进行另一笔付款，则需要再次调用 API 以生成新的比特币地址。

我找到了 find_or_create 方法，但我不确定如何在我的实现中使用它或使用哪种方法来表示 "If it does not exist - do this"

如果已经存在 Payment，我目前的代码可以工作，但如果不存在 Payment，我会收到无效或未知的 method/variable 错误。

If a Payment exists, and the last Payment's amount is 0.0 or nil, just show the last Payment's existing Bitcoin address.

if Payment.exists?
 Payment.last.amount.to_f == 0.0 && Payment.last.amount == nil
 @last_address = Payment.last.btc
 @last_address

Then else if the Payment is greater than 0.0 generate and save a new Bitcoin address.

elsif Payment.present?
 Payment.last.amount.to_f > 0.0
 @new_address = BlockIo.get_new_address
 Payment.create( btc: @new_address['data']['address'] )
  respond_to do |format|
   format.html { redirect_to '/save_btc'}
  end

Else Just generate and save a new Bitcoin address.

else
@new_address = BlockIo.get_new_address
Payment.create( btc: @new_address['data']['address'] )
 respond_to do |format|
  format.html { redirect_to '/save_btc'}
 end
end

如何重构此代码，以及如何使用 find_or_create 或者如果记录不存在，则通过调用 API?

创建一条新记录

用户无需在视图中执行任何操作，因为一旦他们点击“支付”，就会调用运行上述方法的页面。这是我的路线，效果很好：

match '/save_btc' => 'payments#create', via: [:get, :post]

如有任何帮助或意见，我们将不胜感激。提前致谢。

编辑：当没有现有付款时，我收到以下错误：

NoMethodError - undefined method `amount' for nil:NilClass:

显示与 elsif 行相关：Payment.last.amount.to_f > 0.0

NoMethodError - undefined method数量' nil:NilClass： app/controllers/payments_controller.rb:17:in create' actionpack (5.0.0.1) lib/action_controller/metal/basic_implicit_render.rb:4:insend_action' 动作包 (5.0.0.1) lib/abstract_controller/base.rb:188:in process_action' actionpack (5.0.0.1) lib/action_controller/metal/rendering.rb:30:inprocess_action' 动作包 (5.0.0.1) lib/abstract_controller/callbacks.rb:20:in block in process_action' activesupport (5.0.0.1) lib/active_support/callbacks.rb:126:incall' activesupport (5.0.0.1) lib/active_support/callbacks.rb:126:in call' activesupport (5.0.0.1) lib/active_support/callbacks.rb:506:inblock (2 levels) in compile' activesupport (5.0.0.1) lib/active_support/callbacks.rb:455:in call' activesupport (5.0.0.1) lib/active_support/callbacks.rb:455:incall' activesupport (5.0.0.1) lib/active_support/callbacks.rb:101:in __run_callbacks__' activesupport (5.0.0.1) lib/active_support/callbacks.rb:750:in_run_process_action_callbacks' activesupport (5.0.0.1) lib/active_support/callbacks.rb:90:in run_callbacks' actionpack (5.0.0.1) lib/abstract_controller/callbacks.rb:19:inprocess_action' actionpack (5.0.0.1) lib/action_controller/metal/rescue.rb:20:in process_action' actionpack (5.0.0.1) lib/action_controller/metal/instrumentation.rb:32:inblock in process_action' activesupport (5.0.0.1) lib/active_support/notifications.rb:164:in block in instrument'

Answer 1

我已经设法让代码在不存在付款的情况下工作，在我做的 if 块中：

if Payment.exists? && Payment.last.amount.to_f == 0.0 || Payment.exists? && Payment.last.amount == nil

而 elsif 块我只需要将 Payment.present? 更改为 Payment.exists?

这个方案对我来说还是很坑爹的，如果有更好的办法欢迎评论。

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