在EntityFramework 6中，请尝试:

Add-Migration Initial

以便更新初始迁移文件。

问题:你搞砸了你的迁移，你想重置它而不删除现有的表。

问题:您不能重置数据库中现有表的迁移，因为EF希望从头创建表。

应对方法:

Delete existing migrations from Migrations_History table. Delete existing migrations from the Migrations Folder. Run add-migration Reset. This will create a migration in your Migration folder that includes creating the tables (but it will not run it so it will not error out.) You now need to create the initial row in the MigrationHistory table so EF has a snapshot of the current state. EF will do this if you apply a migration. However, you can't apply the migration that you just made as the tables already exist in your database. So go into the Migration and comment out all the code inside the "Up" method. Now run update-database. It will apply the Migration (while not actually changing the database) and create a snapshot row in MigrationHistory.

现在您已经重置了迁移，可以继续进行正常的迁移。

我的问题是手动删除了Migrations文件夹。我这样做是因为我想备份内容，所以我只是将文件夹拖出项目。后来我修复了这个问题，把它放回去(在做了备份副本之后)，然后在解决方案资源管理器中右键单击它并从弹出菜单中选择删除，从而删除了Migrations文件夹。

这个方法不需要删除__MigrationHistory表，所以你不必在部署时把你的手放在数据库上。

从migrations文件夹中删除现有的迁移。 在包管理控制台运行Add-Migration ResetMigrations 清理Up()方法中的迁移历史:

/// <summary>
/// Reset existing migrations by cleaning the __MigrationHistory table
/// and creating a new initial migration with the current model snapshot.
/// </summary>
public partial class ResetMigrations : DbMigration
{
    public override void Up()
    {
        Sql("DELETE FROM [dbo].[__MigrationHistory]");
    }

    public override void Down()
    {
    }
}

在EntityFramework 6中，请尝试:

Add-Migration Initial

以便更新初始迁移文件。

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