2使用相同的查询获取数据时出现Gridview错误 [英] 2 Gridview error on getting data with the same querry

问题描述

我在这里遇到了问题.我想设置两个gridview的数据，它们之间的唯一区别是参数.我的问题是我运行时出现错误.
这是我的代码

hi guys, ive got a problem here. I want to set the data of two gridview where the only difference between them is parameters. my problem is ive got error when i run it.
here is my code

<pre lang="vb">If (IsPostBack = False) Then
    Dim strSQL As String
    Dim strSQL2 As String
    Dim connection As SqlClient.SqlConnection = New SqlClient.SqlConnection("Data Source=ML0003135586;Initial Catalog=TestSQL;Integrated Security=True")
    strSQL = "SELECT [ID], [CourseTitle], [CourseCode], [Objectives], [Duration] FROM [tblTrainingPlan]WHERE ([Category] = @Category)"
    connection.Open()
    Dim myCommand As SqlClient.SqlCommand = New SqlClient.SqlCommand(strSQL, connection)
    myCommand.Parameters.AddWithValue("@Category", lblGEE.Text)
    GridView1.DataSource = myCommand.ExecuteReader()
    GridView1.DataBind()
    myCommand.Dispose()
    strSQL2 = "SELECT [ID], [CourseTitle], [CourseCode], [Objectives], [Duration] FROM [tblTrainingPlan]WHERE ([Category] = @Category)"
    Dim myCommand2 As SqlClient.SqlCommand = New SqlClient.SqlCommand(strSQL2, connection)
    myCommand2.Parameters.AddWithValue("@Category", lblCross.Text)
    TPCross.DataSource = myCommand2.ExecuteReader()
    TPCross.DataBind()
    connection.Close()
    connection.Close()

香港专业教育学院有这样一个错误说

Ive got an error saying like this one

<br />
<br />
There is already an open DataReader associated with this Command which must be closed first.

并指出

TPCross.DataSource = myCommand2.ExecuteReader()

有什么错误?我有逻辑错误吗?
请帮助.在此先感谢

what is the error? do i have a logical error?
Plss help. thanks in advance

推荐答案

由于此列相同，因此可以在其中使用并集.

用这种方式实现

Since this the same column you can use union all in this.

make it this way

strSQL = "SELECT [ID], [CourseTitle], [CourseCode], [Objectives], [Duration] FROM [tblTrainingPlan]WHERE ([Category] = @Category) union all SELECT [ID], [CourseTitle], [CourseCode], [Objectives], [Duration] FROM [tblTrainingPlan]WHERE ([Category] = @Category2) "

<pre lang="vb">connection.Open()
Dim myCommand As SqlClient.SqlCommand = New SqlClient.SqlCommand(strSQL, connection)
myCommand.Parameters.AddWithValue("@Category",lblGEE.Text)
myCommand.Parameters.AddWithValue("@Category2", lblCross.Text)
GridView1.DataSource = myCommand.ExecuteReader()
GridView1.DataBind()
myCommand.Dispose()</pre>

好吧，这是因为DataReader是连接模式，只能转发内容.只要阅读器处于打开状态，连接就处于活动状态并正在工作.因此，如果您尝试使用其他阅读器，则会出现错误.

看看这些:
建议采用变通方法 [类似的讨论 [此处 [

Well, it''s because DataReaders are connected-mode, forward only thing. As long as a reader is open, connection is active and working on it. Thus if you try to use another reader then, you get the error.

Have a look at these:
MSDN blog describing the same in much more detail[^]
Workaround suggested with implication[^]
Similar discussion[^]

If needed, look here[^] for more.

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