C＃中的LINQ错误味精＆QUOT;无法找到源类型的查询模式的实现“翻番？”。 '选择'未找到 [英] C# Linq error msg "could not find an implementation of the query pattern for source type 'double?'. 'Select' not found

问题描述

我想建立一个简单的银行应用程序，当用户进行存款，增加了兴趣。我有一个接受存款金额，当提交被点击的计算将发生在Web窗体的文本框。但我得到的无法找到源类型双？查询模式的实现。选择未找到。消息在我的code。平衡被声明为双？在会计类。有很多的解决方案，我看到的是已经在顶部添加使用System.Linq的命名空间，但我已经这样做了。

 公共无效GetInterest（）
        {            变种DB =新CelticSavingsBank.Classes.Accounts（）;            VAR myBalance =从在db.Balance
                             选择一个;
                db.Balance = myBalance +（myBalance * 0.03）;        }        保护无效depositButton_Click（对象发件人，EventArgs的发送）
        {
            GetInterest（）;
        }
 

解决方案

db.Balance 是翻番？

除非你有一个非常奇怪的集扩展方法，你只能运行在LINQ查询一个的集的;即的IEnumerable＆LT; T＆GT;

I am trying to set up a simple banking application that adds interest when the user makes a deposit. I have a textbox on the webform that accepts the deposit amount and when "Submit" is clicked the calculation will take place. however I get the "could not find an implementation of the query pattern for source type 'double?'. 'Select' not found." message in my code. Balance is declared as a double? in the Accounts class. A lot of solutions I saw already were to add the using System.Linq namespace at the top but I've already done that.

public void GetInterest()
        {

            var db = new CelticSavingsBank.Classes.Accounts(); 

            var myBalance = from a in db.Balance
                             select a;
                db.Balance = myBalance + (myBalance * 0.03);    

        }

        protected void depositButton_Click(object sender, EventArgs e)
        {
            GetInterest();
        }

解决方案

db.Balance is a double?.

Unless you have a very weird set of extension method, you can only run LINQ queries over a collection; namely, IEnumerable<T>.

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