这里记录一个在使用.net core中ef core执行数据库操作时遇到的问题: 我在代码中使用DbContext下的Update方法准备将更改后的数据像这样步到数据库: _context.Menus.Update(menu); 这是很常见的用法,但没想到一直报如下错误: The instance of entity type 'Menu' cannot be tracked because another instance with the same key value for {'Id'}…

一.问题描述 问题:The instance of entity type 'xxxx' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is atta…

加上AsNoTracking. 人不能两次踏入同一条河. 我 就踏入了.o(╥﹏╥)o…

最近在用ASP.NET CORE时遇到一些问题,现记录下: 出现上述错误,即在更新实体数据时出现的错误 services.AddDbContext<StoreContext>(c => c.UseInMemoryDatabase(Guid.NewGuid().ToString()).UseQueryTrackingBehavior(QueryTrackingBehavior.NoTracking));…

本文转自:http://stackoverflow.com/questions/6033638/an-object-with-the-same-key-already-exists-in-the-objectstatemanager-the-object cannot be tracked because another instance of this type with the same key is already being tracked If you load the entity…

今天在进行代码检查的时候出现下面的异常: type parameters of <T>T cannot be determined; no unique maximal instance exists for type variable T with upper bounds int,java.lang.Object 当时的第一感觉就是代码因为jdk版本太低引起的. 因为最后咨询了配置管理组的同事,确实发现是因为我本地jdk用的是1.7版本,而代码检查机器上用的是jdk1.6版本.因此出现了这…

今天遇到了一个奇葩问题,虽然解决了,但还是一脸懵,先附赠一下别人的解决方案:https://www.cnblogs.com/zwjaaron/archive/2012/06/08/2541430.html(我是参考这篇文章解决的,但是问题不一样). 先描述一下我的问题吧: 我们的项目的发布流程是,本地开发完成,提交测试环境,测试完成,提交业务测试环境,最终上线.前情提要:我们的新版本开发完成了,但是测试时间充裕,我们就进行了下一个迭代的开发,作为一个严肃的开发者,自己已经经过了测试环境的自测.然…

背景 有一个 Flask 项目,然后有一个路由返回的是 dict 通过浏览器访问,结果报错 关键报错信息 TypeError: 'dict' object is not callable The view function did not return a valid response. The return type must be a string, tuple, Response instance, or WSGI callable, but it was a dict. 意思是不能返回…

问题: https://q.cnblogs.com/q/98333/ Msg表(Id,Content,IsDel).内有 virtual ICollection<MsgDetail> MsgDetails属性 MsgDetail表(Id,MsgId,SubContent,IsDel) 两者是一对多关系. 如何进行如下意思的的筛选? 若写这句伪代码: context.Msg.First(t=>t.Id==1).Include(t=>t.MsgDetail.Where(t=>t.…

这是在网站里遇到的一个错误,自动生成的不能手动添加, reference: http://stackoverflow.com/questions/19695545/the-entity-type-xxx-is-not-part-of-the-model-for-the-current-context When I created a strong view using the Quickfix context it blew up, because it was trying to associ…

背景:EF Core项目中使用InMemory作为数据库提供程序,编写单元测试. 报错:“The instance of entity type 'Movie' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity ins…

1.在数据库中新建两张测试表 创建用户表 use eftest go if exists(select * from sysobjects where name='UserInfo') drop table UserInfo create table UserInfo( ID ,) primary key, UserName ) not null, Sex ) default '男', age int ) go 创建订单表 use eftest go if exists (select * fr…

前言 通过我发表的博文可知最近一段时间会将持续讲解EntityFramework Core特性,在此之前我提到过Backing Fields,回头翻了翻感觉写的还不够好,于是乎再来讲解一番,也是自己再一次巩固,废话少说,开门见山. EntityFramework Core Backing Fields基础 Backing Fields特性出现于EF Core 1.1,我们姑且将其翻译为返回字段,这样翻译和实际作用对应,Backing Fields允许EF Core读或者写到一个字段而非属性,说的…

1. 开发时是在Mac+MySql, 尝试发布时是在SQL2005+Win 2008 (第一版) 在Startup.cs里,数据库连接要改,分页时netcore默认是用offset关键字分页, 如果用SQL2012之前的版本,就要改 //-----Use SqlServer, 默认用offset分页(这个是sql2012版本之后才有的功能) services.AddDbContextPool<CRMContext>( tt => tt.UseSqlServer(Configuration…

在EF Core的DbContext中,我们可以通过DbContext或DbSet的Attach方法,来让DbContext上下文来跟踪(track)一个实体对象,假设现在我们有User实体对象,其UserCode为Key属性: using System; using System.Collections.Generic; using System.ComponentModel.DataAnnotations; namespace EFCoreDB.Entities { public parti…

The instance of entity type 'Book' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Cons…

2015/6/4 Open CASCADE Technology: IGES Support http://www.opencascade.org/doc/occt­6.7.0/overview/html/user_guides__iges.html 1/35 Table of Contents Introduction Reading IGES Procedure Domain covered Translatable entities Attributes Administrative da…

原文链接:http://www.c-sharpcorner.com/UploadFile/3d39b4/relationship-in-entity-framework-using-code-first-approach-w/ In this article, you will learn about relationships in Entity Framework using the Code First Approach with Fluent API. 在这篇文章中,你将会学习到使用EF…

一点一点学习jobs的各个方面比较长,比较烦,但是应该看完后会对jobs比较好的应用 一.学习准备 开始dbms_job学习前,先认识一个参数job_queue_processes a.job_queue_processes参数决定了job作业能够使用的总进程数.b.当该参数为0值,任何job都不会被执行,建议合理设置该值且至少大于1.c.对于job运行时间也应该尽量合理的设置间隔以及启动时间.d.如果同一时间内运行的Job数很多,过小的参数值导致job不得不进行等待.而过大的参数值则消耗更多的…

单击第一个图标,第一个图标突出显示,单击第二个图标,第一个变灰,第二个突出显示,反之一样.单击history读取历史记录. Controller ZCL_SUS_C_ORDER_CHANGE 1.    DO_INIT method DO_INIT. *CALL METHOD SUPER->DO_INIT *    . if  ZORDERCHANGEMODEL is initial. create object ZORDERCHANGEMODEL. select * from usr02 in…

一.分离查询命令 Separating commands from queries     早期的面向DDD设计方法的难点是如何设计一个类,这个类要包含域的方方面面.通常来说,任务软件系统方法调用可以分为两类:查询和命令.在这里,查询是指一个系统的和个操作,它不会改变系统的任务值,仅返回一些结果.命令的职责是个性系统数据. 如果两组方法都使用相同的域模型,逻辑上可能存在查询和命令分离不明显问题,所以引入新的设计模式. 从域模型到 CQRS     从某种程序度上,CQRS是复杂的域模型设计的一种…

[AttributeUsage(AttributeTargets.Property)] //Models 特性        public class CanWriteAttribute : Attribute        {            public bool CanWrite { get; set; }        }        public System.Data.SqlClient.SqlParameter[] AddParameter<T>(T Models)   …

<!DOCTYPE html> <html lang="en" xmlns:v-bind="http://www.w3.org/1999/xhtml" xmlns:v-model="http://www.w3.org/1999/xhtml" xmlns:v-on="http://www.w3.org/1999/xhtml"> <head> <meta charset="UTF…

java - No enclosing instance is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance of ) - Stack Overflow https://stackoverflow.com/questions/47541459/no-enclosing-instance-is-accessible-m…

本文内容为转载,重新排版以供学习研究.如有侵权,请联系作者删除. 转载请注明本文出处:Professional C# 6 and .NET Core 1.0 - 38 Entity Framework Core ----------------------------------------------------------------------- What's In This Chapter? Introducing Entity Framework Core 1.0 Using Depe…

本文转自:http://www.asp.net/mvc/overview/older-versions/getting-started-with-ef-5-using-mvc-4/creating-an-entity-framework-data-model-for-an-asp-net-mvc-application Creating an Entity Framework Data Model for an ASP.NET MVC Application (1 of 10)   By    …

本文内容为转载,重新排版以供学习研究.如有侵权,请联系作者删除. 转载请注明本文出处:Professional C# 6 and .NET Core 1.0 - Chapter 38 Entity Framework Core ----------------------------------------------------------------------- What’s In This Chapter? Introducing Entity Framework Core 1.0 Us…

http://blogs.msdn.com/b/adonet/archive/2009/05/11/sneak-preview-persistence-ignorance-and-poco-in-entity-framework-4-0.aspx In Entity Framework 3.5 (.NET 3.5 SP1), there are more than a few restrictions that were imposed on entity classes. Entity cla…

第8章 Code First将走向哪里? So far, this book has covered all of the Code First components that reached their final release at the time of writing. There are, however, some notable features that are still in preview at this time that you should be aware of.…

Reading related data¶ 9 of 9 people found this helpful The Contoso University sample web application demonstrates how to create ASP.NET Core 1.0 MVC web applications using Entity Framework Core 1.0 and Visual Studio 2015. For information about the tu…