1.启动迁移 Enable Migrations
Enable-Migrations -MigrationsDirectory "MigrationsOne" -ContextTypeName "MyFirstDb"
MigrationsOne：自定义的migrations文件夹的名字;
MyFirstDb:你的DbContext的名字;
2.添加迁移 Add-Migrations
Add-Migration -ConfigurationTypeName "WebApp.MigrationsOne.Configuration" AddPerson
WebApp.MigrationsOne.Configuration：Configuration文件完整的路径;
AddPerson：自定义迁移文件的名字;
3.更新数据库 Update-Database
Update-Database -ConfigurationTypeName "WebApp.MigrationsOne.Configuration";