Webform（Linq高级查、分页、组合查询）

一、linq高级查

1.模糊查（包含）

 public List<User> Select(string name)
    {
        return con.User.Where(r =>r.UserName.Contains(name)).ToList();
    }

2.查开头

 public List<User> Select(string name)
    {
        return con.User.Where(r => r.UserName.StartsWith(name)).ToList();
    }

3.查结尾

 public List<User> Select(string name)
 {
        return con.User.Where(r => r.UserName.EndsWith(name)).ToList();
    }

4.个数

clist.Count()

5.最大值：Max(r => r.price);

 public decimal? SelectMax()
    {
        return con.car.Max(r => r.price);
    }

6.最小值：Min(r => r.price);

public decimal? SelectMin()
    {
        return con.car.Min(r => r.price);
    }

7.平均值：Average(r => r.price);

public decimal? SelectAvg()
    {
        return con.car.Average(r => r.price);
    }

8.求和：Sum(r => r.price);

 public decimal? SelectSum() { return con.car.Sum(r => r.price); } 

9.排序：

1、OrderBy 按升序对值进行排序。
2、OrderByDescending 按降序对值进行排序
3、ThenBy 按升序执行次要排序。
4、ThenByDescending 按降序执行次要排序。
（1）升序：OrderBy(r => r.price)

  public List<car> orderBy()
    {
        return con.car.OrderBy(r => r.price).ToList();
    }

（2）降序：OrderByDescending(r => r.price)

  public List<car> orderBy()
    {
      
        return con.car.OrderByDescending(r => r.oil).ToList();
    }

二、分页与组合查询

1.分页

public List<User> Select(int count, int number)
    {
        return con.User.Skip(count * (number - 1)).Take(count).ToList();
    }

 public int MaxPageNumber()
    {
        List<User> list = new UserData().Select();
        double nu = list.Count / (Pagecount * 1.0);
        int num = Convert.ToInt32(Math.Ceiling(nu));
        return num;
    }//总页数

   void btn_next_Click(object sender, EventArgs e)
    {
        int NowNumber = Convert.ToInt32(Label2.Text) + 1;
        if (NowNumber > MaxPageNumber())
        {
            return;
        }
        Repeater1.DataSource = new UserData().Select(Pagecount, NowNumber);
        Repeater1.DataBind();

        Label2.Text = NowNumber.ToString();
        DropDownList2.SelectedValue = NowNumber.ToString();

    }//下一页

2.组合查询

void Button2_Click(object sender, EventArgs e)
    {
    using(WebDataContext con=new WebDataContext()){
        var All = con.User.AsEnumerable();
        if (TextBox1.Text.Trim().Length > 0)
        {
            var namelist = con.User.Where(r => r.UserName.Contains(TextBox1.Text.Trim()));

            All = All.Intersect(namelist);
        }

        if (tb_sex.Text.Trim() == "男" || tb_sex.Text.Trim() == "女")
        {
            var sexlist = con.User.Where(r =>Convert.ToBoolean(r.Sex)==(tb_sex.Text.Trim()=="男"?true:false));

            All = All.Intersect(sexlist);
        }

        if (tb_age.Text.Trim().Length > 0)
        {
             int nowyear = DateTime.Now.Year;
            try {
             int age=  Convert.ToInt32(tb_age.Text.Trim());
             int g = nowyear- age;
             DateTime d = Convert.ToDateTime(g.ToString() + "-1-1");
             if (DropDownList3.SelectedValue == ">=")
             {
                 var agelist = con.User.Where(r => Convert.ToDateTime(r.Birthday) >= d);
                 All = All.Intersect(agelist);

             }
             else
             {
                 DateTime dd = Convert.ToDateTime(g.ToString() + "-12-31");
                 var agelist = con.User.Where(r => Convert.ToDateTime(r.Birthday) <= dd);
                 All = All.Intersect(agelist);

             }
            }
            catch{
            }           
        }


        Repeater1.DataSource = All;
        Repeater1.DataBind();
    }
    }