Migation中的更新语句写法，摘要

        public override void Up()
        {
            AlterColumn("dbo.Dispositions", "Property1", c => c.Boolean());
            AlterColumn("dbo.Dispositions", "IsDisposal", c => c.String()); //如果代码没有自动生成，可手动编写修改的字段类型
        }
        
        public override void Down()
        {
            AlterColumn("dbo.Dispositions", "Property1", c => c.String());
            AlterColumn("dbo.Dispositions", "IsDisposal", c => c.String());//如果代码没有自动生成，可手动编写修改的字段类型
        }