Rails的 - 問題重構控制器的嵌套屬性創建

Question

我有型號：

Transaction has_many :credits, :debits 
Credit belongs_to :transaction 
Debit belongs_to :transaction 

每個學分必須有一個平衡的借方，反之亦然。

我目前（成功）具有以下內幕交易的create方法實現這一目標：

@transaction = Transaction.new(params[:transaction]) 

Transaction.transaction do 

    # Balance debits with credits (Sales) 
    if params[:balance_transaction] == 'credit' 
    @transaction.credits.each do |credit| 
     @transaction.debits.push(Debit.new({ 
     :quantity => 0, 
     :cost_per_unit => 0, 
     :description => 'Balancing Debit', 
     :amount => credit.amount, 
     :account_id => 23 #Get from settings in future to allow users to choose Debtor account 
     })) 
    end 
    elsif params[:balance_transaction] == 'debit' 
    @transaction.debits.each do |debit| 
     @transaction.credits.push(Credit.new({ 
     :quantity => 0, 
     :cost_per_unit => 0, 
     :description => 'Balancing Credit', 
     :amount => credit.amount, 
     :account_id => 43 #Get from settings in future to allow users to choose Creditor account 
     })) 
    end 
    else 
    raise ActiveRecord::Rollback # There's no balancing transaction. Don't save it! 
    end 

end 

我試圖通過更換@transactions.credits.push(...) with debit.balancing_credit並把在下面的移動平衡借記/貸記創作到借記/貸記款借記型號：

def balancing_credit 
    transaction.credits.new({ 
    :quantity => 0, 
    :cost_per_unit => 0, 
    :description => 'Balancing Debit', 
    :amount => amount, 
    :account_id => 43 #Get from settings in future to allow users to choose Creditor account 
    }) 
end 

我認爲這是非常簡單的重構，但它拋出了一個undefined method 'debits' for nil:NilClass錯誤。似乎它看起來在數據庫中尚未保存的交易，以創建平衡功勞？難道我做錯了什麼？

Answer 1

你說得對，這樣的機制應該屬於模型，而不是控制器。你可以對你的交易模型before_save回調：

class Transaction 
    after_save :balance_operations 

    def balance_operations 
    if credits 
     credits.each do|credit| 
     debit = debits.build (#do all your stuff here. build() automaticly fills the transaction_id field of your new debit with the proper id) 
     return false unless debit.save 
     end 
    if debits # can use elsif if mutually exclusive conditions 
     # same thing as above 
    end 
    end 
end 

這依賴於一個事實，即回調鏈被包裹在一個ActiveRecord :: Base.transaction。如果回調返回false，ActiveRecord將執行回滾。有關更多信息，請參閱「交易」一章here。

如果您在一次交易中有很多操作，您也可以查看a look at this to improve performance。

編輯：你也可以添加validates_associated :debit, :credits到模型