如果你知道你的数据库和代码是同步的，现在只是挂在一些简单的事情上，比如试图复制任务的迁移，最简单的方法是重新开始迁移而不丢失数据:

删除VS中的Migrations文件夹。 创建一个新的迁移(例如add-migration InitialCreate) 从__efmigrationhistory db中删除除第一行外的所有内容，并将第一行值更改为带有日期代码的第一个迁移名称(例如20220510060015_InitialCreate)

如果您不知道迁移表的ProductVersion，您可以在新创建的Migrations文件夹中的Designer或Snaphot .cs文件中找到它。

现在，当您运行update-database时，它应该不会出错(并且不执行任何任务)。如果您在早期的迁移中进行了大量的重命名、删除、表、列等操作，那么这可能也是为初始生产环境获得最干净的SQL迁移脚本的好方法。

如果您的代码和db不同步，这取决于您处理的数据量和它们不同步的程度，最好执行上面的步骤1和2，然后备份db并删除它，让迁移从头开始重新创建它，然后恢复数据。

微软:管理迁移-重置所有迁移

To avoid the steps above, sometimes if a migration blows up midway through, you have to step through a migration and comment out each migrationBuilder block that's already completed (in the order they were created), especially if it's not clear from the migration error. So you can look at your db and see that tables, columns, FKs, indexes, etc. that have been dropped, renamed, created, etc. and then just go down the list of migrationBuilder blocks and step through the migration (comment out the completed steps, run update-database again, repeat). When you're done, uncomment everything.

如果表中已经有数据，并且您正在尝试添加FK约束，则可能会遇到另一个常见错误:

无法添加或更新子行:外键约束失败 (Database1。# sql -修改- d9b - 445 b,约束 FK_TableA_TableB_TableBId外键(TableBId)引用 表b (' TableBId)

你要创建FK约束的表，它的FK约束列与主表的PK列不匹配。最好提前做好准备，首先创建一个带有默认值占位符的PK表，但是如果您已经收到了错误，那么我们就在这里。解决这个问题以避免上述一些更激烈的步骤的最简单的方法是:

检查是否创建了FK列，是否分配了默认值(例如，在TableA中，FK约束TableBId = "0")。 修改PK表(或先创建它)，使用第一步中分配的默认PK Id记录(例如，在TableB中，创建TableBId = "0"的记录)。 注释掉migrationBuilder之前的所有内容。AddForeignKey块出错并再次运行update-database。迁移现在应该创建FK约束并完成。 取消一切。

VSC(Visual Studio Code) - .Net核心

1.删除状态:删除项目中的迁移文件夹;

2.删除数据库中__MigrationHistory的记录;

3.Dotnet ef数据库drop -v then 您确定要删除服务器上的数据库'<your-database' ?(y / N) 写“N”

4.. dotnet ef迁移添加Initial，然后将20211014110429_initial类的代码写入__MigrationHistory的

如何

Update-Database –TargetMigration: $InitialDatabase

在包管理器控制台?它应该将所有更新重置到非常早期的状态。

参考链接:代码优先迁移-迁移到特定版本(包括降级)

UPDATE 2020 =>重置实体-框架迁移

Add-Migration Initial -Context ApplicationDbContext

ApplicationDbContext =>您的上下文。

但是如果你只需要更新一个存在的标识模式，试试它: https://stackoverflow.com/a/59966100/4654957

对于 EFCore 6/7：

为了将所有更改合并到单个文件中，并将其应用到现有数据库中，同时保留所有数据(即在Production和其他开发中)，以下步骤对我来说很有效:

Delete existing migrations from the Migrations Folder in your project. Delete the Context Snapshop files. I.e. ApplicationDbContextSnapshot.cs, DatabaseContextModelSnapshot.cs or similar. Rebuild your solution Run Add-Migration Initial. (Can be named how you like instead of Initial). This will create a migration in your Migration folder that includes creating the tables, but won't be applied yet. Open the generated Migration file and comment out all the code inside the "Up" method, so that it doesn't make any changes to all your existing tables. (This allows us to update the database in the correct format, without making any changes in the next step) Before the commented code within the Up function, add migrationBuilder.Sql("DELETE FROM [dbo].[__EFMigrationsHistory]"); to have the delete/truncate applied during migration

public partial class Initial : Migration
{
    public override void Up()
    {
        migrationBuilder.Sql("DELETE FROM [dbo].[__EFMigrationsHistory]");
        /*
          OTHER COMMENTED OUT CODE
        */
    }

    public override void Down()
    {
    }
}

Run Update-Database. It will apply the Migration and remove existing migration tracking entriers (while not actually changing the database schema) and create a snapshot row in __EFMigrationsHistory Submit this code and apply to your dev, staging and production databases as you normally would (Ensure the code is still commented out in the Up function, no changes will be applied, except a new entry created in __EFMigrationsHistory) Remove migrationBuilder.Sql("DELETE FROM [dbo].[__EFMigrationsHistory]"); and uncomment all the code from step 5 and submit back to source control. (This way new devs can create the db from scratch. If someone forgot to update their existing database, it'll error out and complain that the tables already exist, so they can just comment the Initial file out and apply.)

在EntityFramework 6中，请尝试:

Add-Migration Initial

以便更新初始迁移文件。