Asp.net mvc 4 代码优先迁移失败

我跟着这个

然后呢

Update-Database -Force -Verbose

这表明它升级了桌子。 但是，显示了一个错误：

The model backing the 'DbConnection' context has changed 
since the database was created.
Consider using Code First Migrations to update the database
(http://go.microsoft.com/fwlink/?LinkId=238269).

我也试过了

Enable-Migrations -ContextTypeName MvcApplication6.Models.DbConnection

但是它说：

Migrations have already been enabled in project 'MvcApplication6'. 
To overwrite the existing migrations configuration, use the -Force parameter.

知道我做错了什么吗？

我找到了解决办法

Database.SetInitializer（null）；

Database.SetInitializer<DbConnection>(null);