1.An operation was scaffolded that may result in the loss of data. Please review the migration for accuracy.

 上次执行还是可以的 这次迁移就提示，常见的解决方案如下：

（1）提交上次更改到数据库后，再进行本次操作，再提交数据库

（2）还原实体，确保数据库和实体保持一致。再去修改实体和进行本次操作，再提交数据库

（3）删除上次的迁移记录 重新迁移。

 实体变更后都要提交数据库确保数据库和实体一致

2.迁移更新提示

手工创建了迁移记录表解决：

mysql脚本：

CREATE TABLE `__efmigrationshistory` (
`MigrationId` varchar(95) NOT NULL,
`ProductVersion` varchar(32) NOT NULL,
PRIMARY KEY (`MigrationId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

sqlserver：

CREATE TABLE [dbo].[__EFMigrationsHistory](
[MigrationId] [nvarchar](150) NOT NULL,
[ProductVersion] [nvarchar](32) NOT NULL,
CONSTRAINT [PK___EFMigrationsHistory] PRIMARY KEY CLUSTERED 
(
[MigrationId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO