Rails：更新贷款金额与支付金额

您可以在贷款模式make_payment(amount)中创建一个方法，并从总贷款金额中减去金额。

我会建议你保持支付日志以便稍后跟踪它们。创建属于Loan模型的Payment模型。

当您为一笔不重要的金额进行贷款时，您通常会遇到一个付款计划，该计划将按分期支付。

每次付款都可以通过多次付款进行支付。

所以让我们看看该机型会是什么样子：

class User < ActiveRecord::Base 
    has_many :loans 
    has_many :instalments, through: :loans 
    has_many :payments, through: :loans 
end 
# [int, foreign_key, index] user_id 
# [float] total_amount - does not change! 
class Loan < ActiveRecord::Base 
    belongs_to :user 
    has_many :instalments 
    has_many :payments 
end 
# [int, foreign_key, index] loan_id 
# [float] total_due 
# [float] payed 
# [datetime] due_date 
class Instalment < ActiveRecord::Base 
    belongs_to :loan 
    has_one :user, through: :loan 
    has_many :payments 
end 
# [int, foreign_key, index] instalment_id 
# [float] amount 
class Payment < ActiveRecord::Base 
    belongs_to :instalment 
    has_one :loan, through: :instalment 
    has_one :user, through: :loan 
end 

这似乎过于复杂，但实际上它只是足有某种形式的财务责任。我们可以跟踪用户每月应支付多少费用以及哪些付款与特定分期付款挂钩。如果你真的想要真正使用这个应用程序，你很可能会遇到更多的法律责任要求（除非你是针对瑞士市场）。

让我们讨论一下该应用程序此处流向：

• 当我们创造，我们将创建一个号码，用户必须支付分期付款的贷款。
• 用户每次支付分期付款时，我们都会设置一个挂钩来更新分期付款金额。
• 我们还需要定期检查用户是否按时支付分期付款。

注意，在这个领域模型中，我们没有创造更新后的贷款金额 - 它只是借用他们的原始量的记录（记住，对于会计目的，你应该始终保持数据）。

相反，我们的要搞清楚我们如何剩余的贷款求和instalments.payed柱：

# [int, foreign_key, index] user_id 
# [float] total_amount - does not change! 
class Loan < ActiveRecord::Base 
    belongs_to :user 
    has_many :instalments 
    has_many :payments 
    def payed 
    installments.sum(:payed) 
    end 
    def amount_due 
    total_amount - installments.sum(:payed) 
    end 
end 

这是一种途径，你也将需要的：

resources :users, shallow: true do 
    resources :loans 
end 
resources :loans, only: [], shallow: true do 
    resources :instalments 
end 
resources :instalments, only: [], shallow: true do 
    resources :payments 
end 

$ rake routes

   Prefix Verb URI Pattern          Controller#Action 
      user_loans GET /users/:user_id/loans(.:format)     loans#index 
         POST /users/:user_id/loans(.:format)     loans#create 
     new_user_loan GET /users/:user_id/loans/new(.:format)    loans#new 
      edit_loan GET /loans/:id/edit(.:format)       loans#edit 
        loan GET /loans/:id(.:format)        loans#show 
         PATCH /loans/:id(.:format)        loans#update 
         PUT /loans/:id(.:format)        loans#update 
         DELETE /loans/:id(.:format)        loans#destroy 
     loan_instalments GET /loans/:loan_id/instalments(.:format)    instalments#index 
         POST /loans/:loan_id/instalments(.:format)    instalments#create 
    new_loan_instalment GET /loans/:loan_id/instalments/new(.:format)   instalments#new 
     edit_instalment GET /instalments/:id/edit(.:format)     instalments#edit 
      instalment GET /instalments/:id(.:format)       instalments#show 
         PATCH /instalments/:id(.:format)       instalments#update 
         PUT /instalments/:id(.:format)       instalments#update 
         DELETE /instalments/:id(.:format)       instalments#destroy 
    instalment_payments GET /instalments/:instalment_id/payments(.:format)  payments#index 
         POST /instalments/:instalment_id/payments(.:format)  payments#create 
new_instalment_payment GET /instalments/:instalment_id/payments/new(.:format) payments#new 
      edit_payment GET /payments/:id/edit(.:format)      payments#edit 
       payment GET /payments/:id(.:format)       payments#show 
         PATCH /payments/:id(.:format)       payments#update 
         PUT /payments/:id(.:format)       payments#update 
         DELETE /payments/:id(.:format)       payments#destroy