linq分页组合查询

一、linq高级查

1.模糊查（字符串包含）

1  public List<User> Select(string name)
2     {
3         return con.User.Where(r =>r.UserName.Contains(name)).ToList();
4     }

2.查开头（StartsWith,以XX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.查出来的数组长度（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)

1   public List<car> orderBy()
2     {
3         return con.car.OrderBy(r => r.price).ToList();
4     }

（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

1 public List<User> Select(int count, int number)
2     {
3         return con.User.Skip(count * (number - 1)).Take(count).ToList();
4     }//这里的number是当前页数，count是每页的数据条数。skip，除去前多少条数据剩下的数据。take,取几条数据，这句话就是查询除去前多少条之后的剩下的数据的前多少条数据

 public int MaxPageNumber()
    {
        List<User> list = new UserData().Select();
        double nu = list.Count / (Pagecount * 1.0);//不要忘了取上线
        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;//下一页的页数
        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())//using比较适合用于个人开发，当花括号里的内容结束后内存自动释放，节省资源
{
        var All = con.User.AsEnumerable();//AsEnumerale也是一个集合，不会占用系统空间，相当于只是把查询字符串给拼接起来，准备好，
当执行ToList时才会进行查询
        if (TextBox1.Text.Trim().Length > 0)//说明这里填写了内容
        {
            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();
    }
    }

分页组合查（以下一页为例）

 void LinkButton2_Click(object sender, EventArgs e)//下一页
    {
        using (renuanDataContext ren = new renuanDataContext())
        {
            var all = ren.Users.AsEnumerable();
            if (chayhmtext.Text.Trim().Length > 0)
            {
                var namelist = ren.Users.Where(r => r.Uname.Contains(chayhmtext.Text.Trim()));
                all = all.Intersect(namelist);
            }
            if (chasexdrop.Text.Trim().Length > 0)
            {
                var sexlist = ren.Users.Where(r => r.Usex.ToString() == chasexdrop.SelectedValue);
                all = all.Intersect(sexlist);
            }
            if (chanationdrop.Text.Trim().Length > 0)
            {
                var nationlist = ren.Users.Where(r => r.Unation.ToString() == chanationdrop.Text);
                all = all.Intersect(nationlist);
            }
            count2.Text = Math.Ceiling(all.Count() / (countnum * 1.0)).ToString();//总页数
            int page= Convert.ToInt32(count1.Text) + 1;//点击之后的页数
           if(Convert.ToInt32(count1.Text)< Convert.ToInt32(count2.Text))//判断是否为最后一页
           {
              count1.Text = page.ToString();
              Repeater1.DataSource = all.Skip(countnum * (Convert.ToInt32(count1.Text) - 1)).Take(countnum).ToList();
         
              Repeater1.DataBind();
           }//页数
        }//using
    }