问题是 - 新应用程序，客户想要 Linq，.NET 4.0，许多“类别”和“类型”的数据表 - 通常是两个字段的简单数据表：ID 和名称（或描述）
与其生成一个 Web 表单来编辑这些数据表中的每一个，不如只需要一个网页来编辑所有这些数据表，而您只需选择要编辑的数据表。（顺便说一句 - “模式迷”在哪里。这不是模式吗？模式 .NET 代码模板在哪里？）
我正在玩 Northwinds 数据库。我添加了一个名为 DropDownConfiguration 的表：
USE [Northwind]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[DropDownConfiguration](
[DropDownConfigurationID] [bigint] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](50) NOT NULL,
[TableName] [nvarchar](50) NOT NULL,
[PrimaryKeyName] [nvarchar](50) NOT NULL,
CONSTRAINT [PK_DropDownConfiguration] PRIMARY KEY CLUSTERED
(
[DropDownConfigurationID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
然后我用以下数据填充了这个数据表：
DropDownConfigurationID Name TableName PrimaryKeyName
1 Categories Categories CategoryID
2 Regions Regions RegionID
asp.net 网页看起来像：
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="EditMultiTable.aspx.vb"
Inherits="EditMultiTable" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:LinqDataSource ID="LinqDataSourceMultiTable" runat="server" ContextTypeName="DataClassesDataContext"
EnableInsert="True" EnableUpdate="True" EntityTypeName="" TableName="Categories">
</asp:LinqDataSource>
<asp:DropDownList ID="ddlDropDownConfigurations" runat="server" AutoPostBack="True">
</asp:DropDownList>
<asp:GridView ID="GridViewMultiTable" runat="server" DataKeyNames="CategoryID" DataSourceID="LinqDataSourceMultiTable">
<Columns>
<asp:CommandField ShowEditButton="True" />
</Columns>
</asp:GridView>
</div>
</form>
</body>
</html>
后面的代码如下所示：
Option Explicit On
Option Strict On
Partial Class EditMultiTable
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim myDropDownConfigurationList As List(Of DropDownConfiguration)
If Not Page.IsPostBack Then
' Tell the drop down what data tables we want to be able to edit
myDropDownConfigurationList = GetDropDownConfigurations()
ddlDropDownConfigurations.DataSource = myDropDownConfigurationList
ddlDropDownConfigurations.DataTextField = "Name"
ddlDropDownConfigurations.DataValueField = "DropDownConfigurationID"
ddlDropDownConfigurations.DataBind()
End If
End Sub
Protected Sub ddlDropDownConfigurations_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlDropDownConfigurations.SelectedIndexChanged
Dim myDropDownConfiguration As DropDownConfiguration
Dim myDropDownConfigurationList As List(Of DropDownConfiguration)
If ddlDropDownConfigurations.SelectedIndex > -1 Then
' clear out the old data bindings between the LinqDataSource and the GridView
GridViewMultiTable.DataSourceID = Nothing
GridViewMultiTable.DataSource = Nothing
GridViewMultiTable.DataKeyNames = Nothing
GridViewMultiTable.DataMember = Nothing
GridViewMultiTable.AutoGenerateColumns = False
GridViewMultiTable.AutoGenerateEditButton = False
GridViewMultiTable.DataBind()
GridViewMultiTable.Columns.Clear()
' Set up the LinqDataSource for the new table
myDropDownConfigurationList = GetDropDownConfigurations()
myDropDownConfiguration = (From ddc In myDropDownConfigurationList Where ddc.DropDownConfigurationID = Long.Parse(ddlDropDownConfigurations.SelectedValue) Select ddc).FirstOrDefault()
LinqDataSourceMultiTable.TableName = myDropDownConfiguration.TableName
LinqDataSourceMultiTable.EntityTypeName = String.Empty
LinqDataSourceMultiTable.EnableInsert = True
LinqDataSourceMultiTable.EnableUpdate = True
LinqDataSourceMultiTable.DataBind()
' bind the GridView to the LinqDataSource with the new data table
GridViewMultiTable.DataSourceID = "LinqDataSourceMultiTable"
GridViewMultiTable.DataKeyNames = New String() {myDropDownConfiguration.PrimaryKeyName}
GridViewMultiTable.AutoGenerateColumns = True
GridViewMultiTable.AutoGenerateEditButton = True
GridViewMultiTable.DataBind()
End If
End Sub
' Get my data table that lists the data tables that I want to configure
Function GetDropDownConfigurations() As List(Of DropDownConfiguration)
Dim myDropDownConfigurationList As List(Of DropDownConfiguration)
Using myDataClassesDataContext As New DataClassesDataContext
myDropDownConfigurationList = (From ddc In myDataClassesDataContext.DropDownConfigurations Select ddc).ToList()
End Using
Return myDropDownConfigurationList
End Function
End Class
我的问题是 - LinqDataSource 或 GridView 没有被清除。它使用一个数据表的一半和另一个数据表的一半。这就是为什么在我的代码中 - 我尝试以各种可以想象的方式清除 LinqDataSource 和 GridView。如果我运行程序，在下拉列表框中选择“区域”，然后尝试编辑“区域”的第一行，我收到以下错误：
DataBinding：“Category”不包含名为“RegionID”的属性。说明：执行当前 Web 请求期间发生未处理的异常。请查看堆栈跟踪以获取有关错误及其源自代码的位置的更多信息。
异常详细信息：System.Web.HttpException：DataBinding：“Category”不包含名为“RegionID”的属性。