VB.NET：从 MySQL DB 检索图像（blob）
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VB.NET: Retrive an image (blob) from MySQL DB
提问by Pinturikkio
I've a field called "Foto" in MySQL DB. This field is a blob. When I used SQL Server, the following code worked:
我在 MySQL 数据库中有一个名为“Foto”的字段。该字段是一个 blob。当我使用 SQL Server 时，以下代码有效：
Dim conn As New MySqlConnection
conn.ConnectionString = ConnectionString
Dim cmd As New MySqlCommand
cmd.Connection = conn
conn.Open()
cmd.CommandText = "SELECT Foto FROM MyTable WHERE ID = '" & IDtxt.ToString & "'"
Dim reader As MySqlDataReader
reader = cmd.ExecuteReader
While reader.Read
If (IsDBNull(reader("Foto"))) Then
frmCartaIdentitaView.pctImage.Image = Nothing
Else
Dim byteImage() As Byte = reader("Foto")
Dim frmImageView stmFoto As New System.IO.MemoryStream(byteImage)
frmImageView.pctImage.Image = Image.FromStream(stmFoto)
frmImageView.pctImage.SizeMode = PictureBoxSizeMode.Zoom
frmImageView.Show()
End If
End While
But now that I'm using mysql, is produced the following error: invalid parameter.
但是现在我使用的是mysql，产生了以下错误：参数无效。
回答by Steve
If your ID field is an integer, see if this gets you past that error. Instead of this:
如果你的 ID 字段是一个整数，看看这是否能让你克服那个错误。取而代之的是：
cmd.CommandText = "SELECT Foto FROM MyTable WHERE ID = '" & IDtxt.ToString & "'"
Try this:
尝试这个：
cmd.CommandText = "SELECT Foto FROM MyTable WHERE ID = " & ctype(int32,IDtxt).ToString
回答by Salvatore
I had the same problem. I got this error when the BLOB column was empty, then I solved this way: Sorry, but I found this post just now
我有同样的问题。我在 BLOB 列为空时收到此错误，然后我是这样解决的：抱歉，我刚刚找到了这篇文章
Dim conn As New MySqlConnection
conn.ConnectionString = ConnectionString
Dim cmd As New MySqlCommand
cmd.Connection = conn
conn.Open()
cmd.CommandText = "SELECT Foto, length(Foto) AS picLen FROM MyTable WHERE ID = '" & IDtxt.ToString & "'"
Dim reader As MySqlDataReader
reader = cmd.ExecuteReader
While reader.Read
If (reader("picLen "))=0 Then
frmCartaIdentitaView.pctImage.Image = Nothing
Else
Dim byteImage() As Byte = reader("Foto")
Dim frmImageView stmFoto As New System.IO.MemoryStream(byteImage)
frmImageView.pctImage.Image = Image.FromStream(stmFoto)
frmImageView.pctImage.SizeMode = PictureBoxSizeMode.Zoom
frmImageView.Show()
End If
End While
