CurrentStock = db.BillEntry.Where(b => b.GoodsId == item.GoodsId).Sum(b => (decimal?)b.Qty) ?? 0, 出现这种错误是因为没有获取到数据造成的,可以使用三元判断来操作,注意Sum里的Qty应该可以为空,如果为空则返回0,否则正式返回. 也可以用下面的方法: CurrentStock = db.BillEntry.Where(b => b.GoodsId == item.GoodsId).Selec…

把值类型的系统.布尔的失败是因为物化值是null.结果类型的泛型参数或查询必须使用可空类型. 解决方法: 请确保你查询中的字段值不为空或者做为空判断…

I'm trying to create a 2D array to store some values that don't change like this. const int[,] hiveIndices = new int[,] { {200,362},{250,370},{213,410} , {400,330} , {380,282} , {437, 295} , {325, 405} , {379,413} ,{343,453} , {450,382},{510,395},{46…

x 入职了新公司.最近比较忙...一看博客...更新频率明显少了...罪过罪过... 新公司用ASP.NET MVC 遇上一个错误: Unable to cast object of type 'System.Int32' to type 'System.Array'. 说明: 执行当前 Web 请求期间,出现未经处理的异常.请检查堆栈跟踪信息,以了解有关该错误以及代码中导致错误的出处的详细信息. 异常详细信息: System.InvalidCastException: Unable to ca…

最近在研究.netcore,尝试把前后端完全分离.但是在写接口的时候,Post参数是FromBody的时候报错了 Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[] An unhandled exception has occurred while executing the request. System.InvalidCastException: Unable to cast object of type '…

数据类型Type System Hive supports primitive and complex data types, as described below. See Hive Data Types for additional information. Hive支持原生和复杂数据类型. Primitive Types 原生数据类型 Types are associated with the columns in the tables. The following Primitive t…

使用log4net,在win7上可以正常使用,但是在部分xp电脑上可以生成access数据库,但是无法写数据到mdb 排除了程序原因,怀疑是xp缺少什么dll之类的 偶然查到log4net的调试方法: 第1步: (1)如果是配置在app.confing等confing文件中,在appSettings节点中增加名称为“log4net.Internal.Debug”的节点,并确保值为“true" <configuration> <appSettings> <add ke…

Type system[edit] Main articles: Data type, Type system, and Type safety A type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. The goal of a type system…

1. Unified Type System Scala has a unified type system, enclosed by the type Any at the top of the hierarchy and the type Nothing at the bottom of the hierarchy. All Scala types inherit from Any. # Using Any, Book extends AnyRef, and x is an Int that…

错误: Could not load type 'System.Reflection.AssemblySignatureKeyAttribute' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c 调试或者在安装了VS2012的电脑上运行没事,但在干净的环境下,就报这个错误. 解决: 查了一下AssemblySignatureKeyAttribute,是.net framework4.…