在 VB.NET 中使用 DataReader
我收到错误消息有一个与此命令关联的开放数据读取器，需要首先关闭，使用以下代码：
myCommand = New SqlCommand("SELECT BookCode FROM tblBook",myConnection)
myReader = myCommand.ExceuteReader
While myReader.Read
If myReader(0).ToString <> txtBookCode.Text Then
myCommand = New SqlCommand("INSERT INTO tblBook VALUES(@BookCode, @BookTitle)",myConnection)
myCommand.Parameters.AddWithValue("@BookCode", txtBookCode.Text)
myCommand.Parameters.AddWithValue("@BookTitle", txtBookTitle.Text)
myCommand.ExecuteNonQuery()
Else
MsgBox("There is already a book name '"& txtTitle.Text "'. Please try another code.",vbOkOnly,"BookCode Exists")
End If
End While
请帮助。
I got the error message There is an open data reader associated with this command which needs to be closed first by using the following code:
myCommand = New SqlCommand("SELECT BookCode FROM tblBook",myConnection)
myReader = myCommand.ExceuteReader
While myReader.Read
If myReader(0).ToString <> txtBookCode.Text Then
myCommand = New SqlCommand("INSERT INTO tblBook VALUES(@BookCode, @BookTitle)",myConnection)
myCommand.Parameters.AddWithValue("@BookCode", txtBookCode.Text)
myCommand.Parameters.AddWithValue("@BookTitle", txtBookTitle.Text)
myCommand.ExecuteNonQuery()
Else
MsgBox("There is already a book name '"& txtTitle.Text "'. Please try another code.",vbOkOnly,"BookCode Exists")
End If
End While
Pleas help.
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评论（2）
不要重复使用 myCommand 变量。创建新的。
myCommand 也应该最终被处理（以及 reader）。
异常的真正原因更有可能是您尝试同时在一个连接上运行两个命令。
首先从阅读器读取您需要的所有数据，然后进行所有插入。不是同时两个（我假设你不想创建两个连接。那会很糟糕）
Don't reuse myCommand variable. Create new one.
myCommand should be disposed in the end too (as well as reader).
Real reason of exception is more likely that you're trying to run two command on one connection at the same time.
First read all data you need from reader and THEN do all inserts. Not both at once (i assume you don't want to create two connections. That would suck)
看起来您正尝试在第一行代码和 WHILE 循环内多次使用一个变量 myCommand 。
最好再声明一个 AdoCommand 变量以在 LOOP 中使用它
looks like you're trying to use one variable myCommand more than once - in the first line of code and within a WHILE loop.
it's better to declare one more AdoCommand variable to use it in LOOP