Rails 3 -事务和锁定

Question

我是Rails新手，并且有一个需要处理事务的系统。用户可以输入一个绑定了多个用户的事务。这些用户欠进行交易的人一定数量的钱。例如，比尔可能为4个朋友买午餐，账单是125美元。他们决定把账单分成5份，每人欠25美元。比尔总共输入125美元，并输入每个朋友(包括他自己)欠这笔交易25美元。我在控制器和模型中有代码来实现这个目标，但我真的不知道我是否正确使用事务和锁定。同样，这是在控制器中获得这些信息的最终方式吗?我正在使用事务，因为所有这些操作必须一起发生或失败(原子性)，并且我需要锁定以防多个用户同时尝试提交(隔离)。也许我应该让后台的db处理锁?它已经这样做了吗?比如说，MySQL?谢谢。

<标题> trans_controller.rb h1> tran.rb

class Tran < ActiveRecord::Base
    has_many :transaction_users, :dependent => :destroy, :class_name => 'TransactionUser'
    belongs_to :submitting_user, :class_name => 'User'
    belongs_to :buying_user, :class_name => 'User'
    
    accepts_nested_attributes_for :transaction_users, :allow_destroy => true
    validates :description, :presence => true,
                            :length => {:maximum => 100 }
    #validates :total,      :presence => true
    validates_numericality_of :total, :greater_than => 0
    
    validates :submitting_user_id,      :presence => true               
    validates :buying_user_id,          :presence => true   
            
    #validates_associated :transaction_users
    
    validate :has_transaction_users?
    validate :has_correct_transaction_user_sum?
    validate :has_no_repeat_users?
    
    def update_user_balances
        # Update the buying user in the transaction
        self.buying_user.lock!
        # Update the user's total, since they were in the transction
        self.buying_user.update_attribute :current_balance, self.buying_user.current_balance - self.total
        # Add an offsetting transaction_user for this record
        buying_tran_user = TransactionUser.create!(:amount => -1 * self.total, :user_id => self.buying_user_id, :tran => self)
        #if buying_tran_user.valid?
        #   raise "Error"
        #end
        
        # Loop through each transaction user and update their balances.  Make sure to lock each record before doing the update.
        self.transaction_users.each do |tu|
            tu.user.lock!
            tu.user.update_attribute :current_balance, tu.user.current_balance + tu.amount
        end
    end
    
    def has_transaction_users?
        errors.add :base, "A transcation must have transaction users." if self.transaction_users.blank?
    end
    
    def has_correct_transaction_user_sum?
        sum_of_items = 0;
        
        self.transaction_users.inspect
        self.transaction_users.each do |key|
            sum_of_items += key.amount if !key.amount.nil?
        end
        
        if sum_of_items != self.total
            errors.add :base, "The transcation items do not sum to the total of the transaction." 
        end 
    end
     
    def has_no_repeat_users?
        user_array = []
        self.transaction_users.each do |key|
            if(user_array.include? key.user.email) 
                errors.add :base, "The participant #{key.user.full_name} has been listed more than once."
            end
        
            user_array << key.user.email
        end
    end 
end

Answer 1

我会避免手动执行锁，因为mysql将在事务内部正确处理必要的行级锁。在这种情况下，使用事务是正确的。我要避免的是创建一个局部变量来跟踪事务是否在没有错误的情况下完成:

def create
    @title = "Create Transaction"
    # Add the transaction from the client
    @tran = Tran.new(params[:tran])
    # Update the current user
    @tran.submitting_user_id = current_user.id
    # Update the data to the database
    # This call commits the transaction and transaction users 
    # It also calls a method to update the balances of each user since that isn't
    # part of the regular commit (why isn't it?)
    begin 
        @tran.transaction do
            @tran.save! 
            @tran.update_user_balances
            trans_successful = true
        end 
    rescue
        flash.now[:error] = @tran.errors.full_messages.to_sentence          
        render 'new'
    else
        flash[:success] = 'Transaction was successfully created.'
        redirect_to trans_path
    end
end