以OrganizationUnit為例，進行擴展，加入IsUse屬性
1.創建一個新類，比如ExtendedOrganizationUnit，繼承OrganizationUnit
public class ExtendedOrganizationUnit: OrganizationUnit
{
public bool IsUse { get; set; }
}
2.把ExtendedOrganizationUnit添加到DbContext里
public virtual DbSet<ExtendedOrganizationUnit> ExtendedOrganizationUnits { get; set; }
3.使用ef code first遷移命令
add-migration add_ExtendedOrganizationUnit_table
update-database
成功