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;

}