使用多个/一个下拉列表中的值从数据库中检索数据

Question

我正在尝试将数据绑定到来自 3 个不同下拉列表的网格视图。

用户可以从 1 个 DDL 或 2 个 DDL 或 3 个 DDL 中选择 1 个值，然后将生成 SQL 查询以从数据库中检索数据并将其绑定到我的 GV。

我所需要的只是一个完美的 SQL 查询或一个函数，它将接受从 D1、D2、D3 中选择的值，同时考虑到用户可以从 D1、D2、D3 或 DDL 的倍数中进行选择

<form id="form1" runat="server">
    <div style="height: 265px">
    
        welcome to this page
        <br />
        here u r allowed to search for a car with available attributes
        <br />
        <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="MODELCODE"   ShowHeaderWhenEmpty="True">
            <Columns>
                <asp:BoundField DataField="MODELCODE" HeaderText="MODELCODE" InsertVisible="False" ReadOnly="True" SortExpression="MODELCODE" />
                <asp:BoundField DataField="Manufacturercountry" HeaderText="Manufacturercountry" SortExpression="Manufacturercountry" />
                <asp:BoundField DataField="modelname" HeaderText="modelname" SortExpression="modelname" />
                <asp:BoundField DataField="modelcolor" HeaderText="modelcolor" SortExpression="modelcolor" />
                <asp:BoundField DataField="dailyhirringrate" HeaderText="dailyhirringrate" SortExpression="dailyhirringrate" />
                <asp:BoundField DataField="sellingprice" HeaderText="sellingprice" SortExpression="sellingprice" />
                <asp:BoundField DataField="numberofcars" HeaderText="numberofcars" SortExpression="numberofcars" />
                <asp:BoundField DataField="currentmielage" HeaderText="currentmielage" SortExpression="currentmielage" />
                <asp:BoundField DataField="enginesize" HeaderText="enginesize" SortExpression="enginesize" />
                <asp:BoundField DataField="liecensenumber" HeaderText="liecensenumber" SortExpression="liecensenumber" />
            </Columns>
        </asp:GridView>
        <asp:SqlDataSource ID="SqlDataSource9" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT * FROM [CARMODEL] WHERE (([Manufacturercountry] = @Manufacturercountry) AND ([modelname] = @modelname))">
            <SelectParameters>
                <asp:ControlParameter ControlID="country" DefaultValue="&quot;&quot;" Name="Manufacturercountry" PropertyName="SelectedValue" Type="String" />
                <asp:ControlParameter ControlID="DropDownList2" DefaultValue="&quot;&quot;" Name="modelname" PropertyName="SelectedValue" Type="String" />
            </SelectParameters>
        </asp:SqlDataSource>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:Button ID="Button1" runat="server" Text="buy a car" />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:Button ID="Button2" runat="server" Text="rent a car" />
        <br />
        <br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    
    </div>
    &nbsp;&nbsp;
        <br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; country&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:DropDownList ID="country" runat="server" DataSourceID="SqlDataSource1"   DataTextField="Manufacturercountry" DataValueField="Manufacturercountry"  AppendDataBoundItems ="true">
            <asp:listitem selected="True" text="" value=""></asp:listitem>
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT DISTINCT [Manufacturercountry] FROM [CARMODEL]"></asp:SqlDataSource>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; modelname :&nbsp;
        <asp:DropDownList ID="DropDownList2" runat="server" DataSourceID="SqlDataSource2" DataTextField="modelname" DataValueField="modelname">
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT DISTINCT [modelname] FROM [CARMODEL]"></asp:SqlDataSource>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; color&nbsp;
        <asp:DropDownList ID="DropDownList3" runat="server" DataSourceID="SqlDataSource3" DataTextField="modelcolor" DataValueField="modelcolor" style="margin-left: 12px">
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource3" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT [modelcolor] FROM [CARMODEL]"></asp:SqlDataSource>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; daily H.rate :&nbsp;
        <asp:DropDownList ID="DropDownList4" runat="server" DataSourceID="SqlDataSource4" DataTextField="dailyhirringrate" DataValueField="dailyhirringrate">
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource4" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT [dailyhirringrate] FROM [CARMODEL]"></asp:SqlDataSource>
        <br />
        <br />
        <br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; selling price&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:DropDownList ID="DropDownList5" runat="server" DataSourceID="SqlDataSource5" DataTextField="sellingprice" DataValueField="sellingprice">
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource5" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT [sellingprice] FROM [CARMODEL]"></asp:SqlDataSource>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; E.size&nbsp;
        <asp:DropDownList ID="DropDownList7" runat="server" DataSourceID="SqlDataSource6" DataTextField="enginesize" DataValueField="enginesize">
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource6" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT [enginesize] FROM [CARMODEL]"></asp:SqlDataSource>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; mileage:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:DropDownList ID="DropDownList6" runat="server" DataSourceID="SqlDataSource7" DataTextField="currentmielage" DataValueField="currentmielage">
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource7" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT [currentmielage] FROM [CARMODEL]"></asp:SqlDataSource>
        <asp:DropDownList ID="DropDownList8" runat="server" DataSourceID="SqlDataSource8" DataTextField="liecensenumber" DataValueField="liecensenumber">
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource8" runat="server" ConnectionString="<%$ ConnectionStrings:MALAK1ConnectionString %>" SelectCommand="SELECT [liecensenumber] FROM [CARMODEL]"></asp:SqlDataSource>
        <br />
        <br />
        <asp:Button ID="Button3" runat="server" Text="check for cars" />
        <br />
        <asp:Button ID="Button4" runat="server" Text="Button" />
        <asp:Button ID="Button5" runat="server" style="margin-left: 365px" Text="Button5" />
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:Button ID="Button6" runat="server" style="margin-left: 134px" Text="Button" Width="109px" />
    </form>

 Protected Sub Button5_Click(sender As System.Object, e As System.EventArgs) Handles Button5.Click

    If country.SelectedValue = "" Then
        conn = obj.Connection
        Dim cmd As New SqlCommand("select * from CARMODEL where modelname = @mdn and modelcolor = @mdc and dailyhirringrate = @dhr and sellingprice = @spr  and liecensenumber = @ln", conn)
        cmd.Parameters.AddWithValue("@mdn", DropDownList2.SelectedValue)
        cmd.Parameters.AddWithValue("@mdc", DropDownList3.SelectedValue)
        cmd.Parameters.AddWithValue("@dhr", DropDownList4.SelectedValue)
        cmd.Parameters.AddWithValue("@spr", DropDownList5.SelectedValue)
        cmd.Parameters.AddWithValue("@ln", DropDownList8.SelectedValue)



        Dim dst As New DataSet()
        Dim dt As New DataTable("frmcntry")

        cmd.ExecuteNonQuery()
        cmd.CommandType = CommandType.Text

        Dim dadapt As New SqlDataAdapter(cmd)
        dadapt.Fill(dt)


        GridView1.DataSource = dt
        GridView1.DataBind()
    End If
End Sub

Answer 1

关键是实体数据模型结合 LINQ TO SQL

如果您使用 EDM 将程序设置到您的数据库中，这将变得非常容易。

例子：

using container as new yourEDMContainer
Dim yourquery as IQueryable(Of yourdatatableelementclass) = container.yourtableSet

If DDL1wasselected Then
   yourquery = yourquery.where(Function(v) v.thevalue1tocompare = DDL1value)
End If

If DDL2wasselected Then
   yourquery = yourquery.where(Function(v) v.thevalue2tocompare = DDL2value)
End If

 If DDL3wasselected Then
   yourquery = yourquery.where(Function(v) v.thevalue3tocompare = DDL3value)
End If

Dim your results = yourquery.ToList()   'only at this point the query is resolved and a call to the datbase will be made. 

end using