由于数据库丢弃在MVC中的代码优先方法，所有记录都被删除 [英] All Records got deleted because of Database Drop in code first approach in MVC

问题描述

您好，



因为所有EF根据我们在前端自动创建的类创建数据库，表和列，代码第一种方法。



因此，在创建数据库，表格和专栏后，我在课堂上再添加了一个额外的coloumn。



但是，我得到了以下异常。



EntityFramework.dll中出现System.InvalidOperationException类型的异常，但未在用户代码中处理



附加信息：自创建数据库以来，支持'MvcMusicStoreContext'上下文的模型已更改。考虑使用Code First Migrations来更新数据库（http://go.microsoft.com/fwlink/?



这是因为迁移。



所以，我在Global.asax.cs（Application_Start）中添加了以下行来修复该异常。



数据库。 SetInitializer（new DropCreateDatabaseIfModelChanges< employeedbcontext>（））;



现在工作正常。



但是问题我的现有数据库和表值被删除并创建new为new。我的意思是只有列名可用。



在MVC中表现不错？怎么能我解决了这个问题。

Hello,

as all EF creates database,table and column according our class created in front-end automatically in code first approach.

So, i added one more extra coloumn in my class after creating Data base ,table and column.

But, i got the following exception .

An exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll but was not handled in user code

Additional information: The model backing the 'MvcMusicStoreContext' context has changed since the database was created. Consider using Code First Migrations to update the database (http://go.microsoft.com/fwlink/?

this is because of Migration.

so, i added the follow line in Global.asax.cs(Application_Start) to fix that exception.

Database.SetInitializer(new DropCreateDatabaseIfModelChanges<employeedbcontext>());

now works fine.

But the problem my existing database and table values got dropped and creates new as new with empty . i mean there is just column name only available.

is that good in MVC? how can i fix this problem.

推荐答案

你采取的路由是一个初始化策略，它的行为是以预期的方式。你不想用它来做一个生产数据库，您想要使用的是迁移。



Code First迁移详细描述于：

<一小时EF = http://msdn.microsoft.com/en-us/data/jj591621.aspx> http://msdn.microsoft.com/en-us/data/jj591621.aspx [<一个href =http://msdn.microsoft.com/en-us/data/jj591621.aspxtarget =_ blanktitle =新窗口> ^ ]



您也可以编写自己的初始化，但除非您想开始了解EF如何与数据库交互的杂草，否则我不会沿着这条路走下去。



这里最重要的一课：迁移！=初始化策略

The route that you took is an initialization strategy, and it is behaving in the expected manner. You don't want to use it for a production database, what you'll want to use instead is a Migration.

Code First migrations are described in detail at:
http://msdn.microsoft.com/en-us/data/jj591621.aspx[^]

You can also write your own initialize, but I would not go down that route unless you want to start getting into the weeds of how EF interacts with the database.

The most important lesson here: migrations != initialization strategy

这篇关于由于数据库丢弃在MVC中的代码优先方法，所有记录都被删除的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！