vb.net 错误：该行/列不存在数据
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Error: No data exists for the row/column
提问by user3260683
I get the following error: No data exists for the row/column.
我收到以下错误：No data exists for the row/column。
It should retrieve the image
它应该检索图像
sSql = "SELECT TOP 1 * FROM Attendance ORDER BY Attendance_id DESC"
Dim cmd As New OleDbCommand(sSql, con)
Dim dr As OleDbDataReader = cmd.ExecuteReader()
dr.Read()
lab1id.Text = dr.GetValue(1).ToString
lab1fname.Text = dr.GetValue(2).ToString
lab1lname.Text = dr.GetValue(3).ToString
lab1position.Text = dr.GetValue(4).ToString
lab1subject.Text = dr.GetValue(5).ToString
dr.Close()
sSql = "select Pfile from Faculty where StId = '" & lab1id.Text & "'"
Dim pcmd As New OleDbCommand(sSql, con)
Dim pdr As OleDbDataReader = cmd.ExecuteReader()
pdr.Read()
Dim bits As Byte() = CType(dr("Pfile"), Byte())
Dim memo As New MemoryStream(bits)
Dim myimg As New Bitmap(memo)
imgRetrieve.Image = myimg
pdr.Close()
回答by Bj?rn-Roger Kringsj?
The dr.GetValue(N) is zero-based ordinal. Change your indices:
dr.GetValue(N) 是从零开始的序数。改变你的指数：
While dr.Read()
lab1id.Text = dr.GetValue(0).ToString
lab1fname.Text = dr.GetValue(1).ToString
lab1lname.Text = dr.GetValue(2).ToString
lab1position.Text = dr.GetValue(3).ToString
lab1subject.Text = dr.GetValue(4).ToString
End While
While pdr.Read() ' | you got a typo here. Change `dr` to `pdr`.
Dim bits As Byte() = CType(pdr("Pfile"), Byte())
Dim memo As New MemoryStream(bits)
Dim myimg As New Bitmap(memo)
imgRetrieve.Image = myimg
End While
Consider changing your code to something like this:
考虑将您的代码更改为如下所示：
Using command As OleDbCommand = con.CreateCommand()
command.CommandText = "SELECT TOP 1 * FROM Attendance ORDER BY Attendance_id DESC;"
Using reader As OleDbDataReader = command.ExecuteReader()
While reader.Read()
lab1id.Text = reader.Item("id").ToString
lab1fname.Text = reader.Item("fname").ToString
lab1lname.Text = reader.Item("lname").ToString
lab1position.Text = reader.Item("position").ToString
lab1subject.Text = reader.Item("subject").ToString
End While
End Using
End Using
Using command As OleDbCommand = con.CreateCommand()
command.CommandText = "select Pfile from Faculty where StId = @StId;"
command.Parameters.AddWithValue("@StId", lab1id.Text)
Using reader As OleDbDataReader = command.ExecuteReader()
While reader.Read()
Dim bits As Byte() = CType(reader.Item("Pfile"), Byte())
Using stream As New MemoryStream(bits)
imgRetrieve.Image = Bitmap.FromStream(stream)
End Using
End While
End Using
End Using
回答by ekad
The problem is you never execute pcmd, see the following two lines:
问题是你从不执行pcmd，看下面两行：
Dim pcmd As New OleDbCommand(sSql, con)
Dim pdr As OleDbDataReader = cmd.ExecuteReader() ' cmd should be replaced with pcmd
I would suggest adding While...End While Statementwhen getting the values from drand pdr. You also need to parameterize the second query to avoid SQL Injection.
我建议在从drand获取值时添加While...End While Statementpdr。您还需要参数化第二个查询以避免SQL 注入。
sSql = "SELECT TOP 1 * FROM Attendance ORDER BY Attendance_id DESC"
Dim cmd As New OleDbCommand(sSql, con)
Dim dr As OleDbDataReader = cmd.ExecuteReader()
While dr.Read()
lab1id.Text = dr.GetValue(1).ToString
lab1fname.Text = dr.GetValue(2).ToString
lab1lname.Text = dr.GetValue(3).ToString
lab1position.Text = dr.GetValue(4).ToString
lab1subject.Text = dr.GetValue(5).ToString
End While
dr.Close()
sSql = "select Pfile from Faculty where StId = @StId"
Dim pcmd As New OleDbCommand(sSql, con)
pcmd.Parameters.AddWithValue("@StId", lab1id.Text)
Dim pdr As OleDbDataReader = pcmd.ExecuteReader()
While pdr.Read()
Dim bits As Byte() = CType(dr("Pfile"), Byte())
Dim memo As New MemoryStream(bits)
Dim myimg As New Bitmap(memo)
imgRetrieve.Image = myimg
End While
pdr.Close()
