降级（回滚）数据库，在生产环境中以代码优先 [英] Downgrade (Rollback) Database with code-first in production environment

问题描述

我有一个Web应用程序，我安装在我的客户的电脑内部使用。我使用C＃MVC5和代码优先实体框架。我使用自动迁移= true，但我停止并将其设置为false。我将其安装在生产环境（发布） - 使用deploy-package（无Visual Studio）。

我有一个客户与应用程序 - 版本1.现在我要升级到版本2.我想启用升级应用程序的数据库（在生产文件中，使用CMD安装从一个包），但有可能降级数据库，如果会有任何问题 - 但不删除现有行。

例如 - 如果我有一个表项目和项目有键，名称，位置。升级时，我添加一个新列：电子邮件。降级 - 新列将被删除。
我在Visual Studio上创建了迁移我得到这个代码（只是为了示例 - 我有更多的迁移）：

  public partial class AddEmail：DbMigration 
 {
 public override void Up（）
 {
 AddColumn（dbo.Items，Email，c => c。串（））; 
} 
 
 public override void Down（）
 {
 DropColumn（dbo.Items，Email）; 
} 
} 
  

现在，我在现有的版本，它工作正常 - 新列已添加，它与新代码一起工作。我添加了几个项目（行）。

现在，如何重新安装旧版本，以便新列被删除？实际上我想回滚新的迁移 - 但是我不想丢失新的行，只有新列。

解决方案

在这篇文章中，有一个解释如何创建脚本从一个迁移迁移到另一个迁移 - 升级或降级。
所以我运行在包管理器控制台 -

更新数据库-Script -TargetMigration：MyMigration1

并获得SQL脚本。

我需要通过它修复一下，然后我刚刚在生产数据库中运行它来降级数据库。

I have a web application that I install on my customers' computers for their inner use. I use C# MVC5 and code-first Entity Framework. I used automatic migration=true but I stopped and set it to false. I installed it on a production environment (release) - with a deploy-package (no Visual Studio).

I have a customer with the application - version 1. Now I want to upgrade to version 2. I want to enable to upgrade the App's DB (in production file, with CMD installation from a package), but to have the possibility to downgrade the DB if there'll be any problems - but without deleting the existing rows.

For example - if I have a table "Items" and Items has Key, Name, Location. On upgrade I add a new column: Email. On downgrade - the new column will be deleted. I created the migration on Visual Studio I get this code (It's just for the example - I have more migrations):

public partial class AddEmail : DbMigration
    {
        public override void Up()
        {
            AddColumn("dbo.Items", "Email", c => c.String());
        }

        public override void Down()
        {
            DropColumn("dbo.Items", "Email");
        }
    }

Now, I installed the App's new version on the existing version and it worked fine - the new column was added and it worked with the new code. I added a few items (rows).

Now, how can I re-install the old version so the new column will be deleted? Actually I want to rollback the new migrations - but I don't want to lose the new rows, only the new columns.

解决方案

In this article there is an explanation how to create a script that migrate from one migration to another - upgrade or downgrade. So I ran in the Package Manager Console -

Update-Database -Script -TargetMigration: MyMigration1

and got the SQL script.

I needed to go through it a fix it a little and then I just ran it on the Production Database to downgrade the DB.

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