webform---组合查询&流水号生成

public partial class 组合查询 : System.Web.UI.Page
{
    private MyDBDataContext _Context = new MyDBDataContext();

    //绑定数据车辆系列
    private void FillBrand()
    {
        List<Brand> list = _Context.Brand.ToList();
        ddlBrand.DataSource = list;
        ddlBrand.DataTextField = "Brand_Name";
        ddlBrand.DataValueField = "Brand_Code";
        ddlBrand.DataBind();
    }
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            FillBrand();
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        var query1 = _Context.Car.AsQueryable();//根据车名查
        var query2 = _Context.Car.AsQueryable();//根据系列查
        var query3 = _Context.Car.AsQueryable();//根据油耗查

        //根据填写情况完善以上三个查询条件
        if (txtName.Text.Trim().Length > 0)
        {
            query1 = query1.Where(p=>p.Name .Contains(txtName.Text));
        }
        if (ddlBrand.SelectedValue != "-1")
        {
            query2 = query2.Where(p=>p.Brand == ddlBrand.SelectedValue);
        }
        if (txtOil.Text.Trim().Length > 0)
        {
            query3 = query3.Where(p=>p.Oil == Convert.ToDecimal( txtOil.Text ));
        }

        //三个查询关系可用集合的交集来实现
        var query = query1.Intersect(query2).Intersect(query3);

        //数据绑定 显示
        Repeater1.DataSource = query;
        Repeater1.DataBind();
    }
}

//点击生成流水号按钮

    protected void Button2_Click(object sender, EventArgs e)
    {
        string prefix = "p" + DateTime.Now.ToString("yyyyMMdd");  //生成当天的流水号前缀
        //查当天的最大流水号(a.已经有流水号 b.没有流水号)
        int maxFlow = 0;
        var query = _Context.Info.Where(p => p.Code.StartsWith(prefix));  //模糊查询当天所有的流水号
        if (query.Count() > 0)  //已有流水号,则找最大流水号
        {
            query = query.OrderByDescending(p=>p.Code);  //按流水号降序排
            string maxCode = query.First().Code;  //获取最大流水号
            maxFlow = Convert.ToInt32(maxCode.Substring(maxCode.Length-3));  //截取并转换出现有的最大的流水号来
        }
        

        //组合生成新的流水号
        string flowCode = prefix + (maxFlow + 1).ToString("000");

        //显示在文本框中
        TextBox1.Text = flowCode;

    }