C# EF Core迁移数据库-编程知识

C# EF Core迁移数据库

现象：

在CodeFirst时，先写字段与表，创建数据库后，再添加内容

但字段与表会变更，比如改名·删除·增加等

需求：

当表字段变更时，同时变更数据库，执行数据库迁移

核心命令

Add-Migration firstMigration

update-database

步骤

打开程序包管理窗口

工具=>NuGet包管理器=>程序包管理控制台

Add-Migration代表迁移命令：后边参数为名称

输入命令:

Add-Migration firstMigration

但是可能会报错,提示EntityFramework的程序包未安装

Your target project 'ShangShangQian' doesn't reference EntityFramework. This package is required for the Entity Framework Core Tools to work. Ensure your target project is correct, install the package, and try again.

NuGet安装下

安装完毕，再执行Add-Migration firstMigration

No migrations configuration type was found in the assembly 'ShangShangQian'. (In Visual Studio you can use the Enable-Migrations command from Package Manager Console to add a migrations configuration).

在程序集“ShangShangQian”中找不到迁移配置类型。（在Visual Studio中，可以使用Package Manager控制台中的“启用迁移”命令添加迁移配置）。

再去执行：启用迁移”命令

Enable-Migrations

哦……可能得加个数据库上下文，就是你继承DbContext的类

再执行下Enable-Migrations -ContextTypeName 加上命名空间与类名

Enable-Migrations -ContextTypeName ShangShangQian.EFCore.DataBaseContext

Checking if the context targets an existing database...
System.ArgumentException: The type 'DataBaseContext' does not inherit from DbContext. The DbMigrationsConfiguration.ContextType property must be set to a type that inherits from DbContext

The type 'DataBaseContext' does not inherit from DbContext. The DbMigrationsConfiguration.ContextType property must be set to a type that inherits from DbContext.

正在检查上下文是否以现有数据库为目标。。。

系统ArgumentException：类型“DataBaseContext”不是从DbContext继承的。DbMigrationsConfiguration。ContextType属性必须设置为从DbContext继承的类型。

继承了啊，奇了怪了…………

Goole下=>缺个 Microsoft.EntityFrameworkCore.Tools 装下

再执行添加启用迁移命令:

Enable-Migrations -ContextTypeName ShangShangQian.EFCore.DataBaseContext

Both Entity Framework Core and Entity Framework 6 are installed. The Entity Framework Core tools are running. Use 'EntityFramework6\Enable-Migrations' for Entity Framework 6.
Enable-Migrations is obsolete. Use Add-Migration to start using Migrations.

实体框架核心和实体框架6都已安装。实体框架核心工具正在运行。对实体框架6使用“EntityFramework6\启用迁移”。

“启用迁移”已过时。使用“添加迁移”开始使用迁移。

=======》去你姥姥的，坑我，这不回到了起点《=======

Add-Migration firstMigration

死马当活马医吧，执行试试

再跑下更新命令？

update-database

表模型变更，执行这俩行，去测试下把表和字段增加·删除·试试，哦报错了……

Failed executing DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
CREATE TABLE "Chats" (
"ChatID" INTEGER NOT NULL CONSTRAINT "PK_Chats" PRIMARY KEY AUTOINCREMENT,
"FromID" INTEGER NOT NULL,
"ToID" INTEGER NOT NULL,
"Message" TEXT NOT NULL,
"Type" INTEGER NOT NULL,
"IsRead" INTEGER NOT NULL,
"SendTime" TEXT NOT NULL,
"ReadTime" TEXT NOT NULL,
"IsPushFrom" INTEGER NOT NULL,
"IsPushTo" INTEGER NOT NULL
);

SQLite Error 1: 'table "Chats" already exists'.