C#-WebForm-LinQ-条件精确查询、高级查询

前台界面，并在后台绑定数据

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Cars.aspx.cs" Inherits="Cars" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            Name:<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
            Brand:<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
            Oil:
        <asp:DropDownList ID="DropDownList1" runat="server">
            <asp:ListItem Value="=">等于</asp:ListItem>
            <asp:ListItem Value=">=">大于</asp:ListItem>
            <asp:ListItem Value="<=">小于</asp:ListItem>
        </asp:DropDownList>
            <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
            Price:
        <asp:DropDownList ID="DropDownList2" runat="server">
            <asp:ListItem Value="=">等于</asp:ListItem>
            <asp:ListItem Value=">=">大于</asp:ListItem>
            <asp:ListItem Value="<=">小于</asp:ListItem>
        </asp:DropDownList>
            <asp:TextBox ID="TextBox4" runat="server"></asp:TextBox>
            <asp:Button ID="Button1" runat="server" Text="查询" />
            <br />
            <br />

            <table style=" 100%; text-align: center;" border="1" cellpadding="0" cellspacing="0">
                <tr style="background-color: navy; color: white;">
                    <td>Code</td>
                    <td>Name</td>
                    <td>Brand</td>
                    <td>Time</td>
                    <td>Oil</td>
                    <td>Powers</td>
                    <td>Exhaust</td>
                    <td>Price</td>
                    <td>Pic</td>
                </tr>
                <asp:Repeater ID="Repeater1" runat="server">
                    <ItemTemplate>
                        <tr>
                            <td><%#Eval("Code") %></td>
                            <td><%#Eval("Name") %></td>
                            <td><%#Eval("Brand") %></td>
                            <td><%#Eval("Time") %></td>
                            <td><%#Eval("Oil") %></td>
                            <td><%#Eval("Powers") %></td>
                            <td><%#Eval("Exhaust") %></td>
                            <td><%#Eval("Price") %></td>
                            <td><%#Eval("Pic") %></td>
                        </tr>
                    </ItemTemplate>
                </asp:Repeater>
            </table>

        </div>
    </form>
</body>
</html>

前台界面代码

条件查询：Lambda表达式 Repeater1.DataSource = con.Car.Where(r => r.Name == name);

比如按照Name进行精确查询

public partial class Cars : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            using (CarDataContext con = new CarDataContext())
            {
                Repeater1.DataSource = con.Car;
                Repeater1.DataBind();
            }
        }
        //<查询>按钮
        Button1.Click += Button1_Click;
    }
    //<查询>按钮
    void Button1_Click(object sender, EventArgs e)
    {
        //Name文本框
        string name = txt_name.Text;
        //对数据库进行操作
        using (CarDataContext con = new CarDataContext())
        {
            //有条件时查询满足条件的数据
            if (name.Length > 0)
            {
                Repeater1.DataSource = con.Car.Where(r => r.Name == name);
            }
            //无条件时查询全部数据
            else
            {
                Repeater1.DataSource = con.Car;
            }
            Repeater1.DataBind();
        }
    }

}

条件精确查询

多条件查询：Repeater1.DataSource = con.Car.Where(r => r.Name == name && r.Price == Convert.ToDecimal(price)).ToList();

public partial class Cars : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            using (CarDataContext con = new CarDataContext())
            {
                Repeater1.DataSource = con.Car;
                Repeater1.DataBind();
            }
        }
        //<查询>按钮
        Button1.Click += Button1_Click;
    }
    //<查询>按钮
    void Button1_Click(object sender, EventArgs e)
    {
        //Name文本框
        string name = txt_name.Text;
        string price = txt_price.Text;
        //对数据库进行操作
        using (CarDataContext con = new CarDataContext())
        {
            //有条件时查询满足条件的数据
            if (name.Length > 0)
            {
                Repeater1.DataSource = con.Car.Where(r => r.Name == name && r.Price == Convert.ToDecimal(price));
            }
            //无条件时查询全部数据
            else
            {
                Repeater1.DataSource = con.Car;
            }
            Repeater1.DataBind();
        }
    }

}

多条件精确查

高级查询：

一、模糊查询（包含字符串）

Repeater1.DataSource = con.Car.Where(r => r.Name.Contains(name)).ToList();

二、开头、结尾

Repeater1.DataSource = con.Car.Where(r => r.Name.StartsWith(name)).ToList();

Repeater1.DataSource = con.Car.Where(r => r.Name.EndsWith(name)).ToList();

三、最大值、最小值

//模糊查询并绑定数据

IQueryable<Car> clist = con.Car.Where(r => r.Name.Contains(name)).AsQueryable();

Repeater1.DataSource = clist;

//展示数据个数

Label1.Text = clist.Max(r => r.Price).ToString();

//展示数据中最小的

Label2.Text = clist.Min(r => r.Price).ToString();

四、个数

//模糊查询并绑定数据

IQueryable<Car> clist = con.Car.Where(r => r.Name.Contains(name)).AsQueryable();

Repeater1.DataSource = clist;

//展示数据个数

Label1.Text = clist.Count().ToString();

五、平均值、和

平均值：Average

Label1.Text = con.Car.Average(r => r.Price).ToString();

和：Sum

Label1.Text = con.Car.Sum(r => r.Price).ToString();

六、升序、降序

升序：

Repeater1.DataSource = con.Car.OrderBy(r => r.Price);

降序：

Repeater1.DataSource = con.Car.OrderByDescending(r => r.Price);

分段排序 - ThenBy()

IQueryable<Car> clist = con.Car.AsQueryable().OrderBy(r => r.Brand).ThenBy(r => r.Oil);