VB.NET：從MySQL DB返回一個圖像（blob）

Question

我在MySQL DB中有一個名爲「Foto」的字段。這個領域是一個blob。當我使用SQL Server中，下面的代碼工作：

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 

但現在，我正在使用MySQL，產生以下錯誤：無效的參數。

Answer 1

如果你的ID字段是一個整數，看看這是否讓你過去的錯誤。取而代之的是：

cmd.CommandText = "SELECT Foto FROM MyTable WHERE ID = '" & IDtxt.ToString & "'" 

試試這個：

cmd.CommandText = "SELECT Foto FROM MyTable WHERE ID = " & ctype(int32,IDtxt).ToString 

Answer 2

我有同樣的問題。我得到這個錯誤時，BLOB列是空的，然後 我解決了這個辦法： 很抱歉，但我發現這個職位剛纔

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