Question

我有一个使用vb.net的桌面应用程序，用于处理一些excel文件，这些文件存储在sql server数据库中。这是我的代码：

Try
        conDCS.Open()
        comDCS.Connection = conDCS
        comDCS.CommandType = CommandType.Text
        comDCS.CommandText = "select top 2 [Filename], [File] " & _
                            "from tblFiles (nolock) " & _
                            "where ([Filename] like 'DIG%' or [Filename] like 'FAC%') and " & _
                            "(UploadDate>='" & FromDate & "' and UploadDate<'" & ToDate & "')"
        comDCS.ExecuteNonQuery()
        rdrDCS = comDCS.ExecuteReader
        If rdrDCS.HasRows Then
            While rdrDCS.Read
                Dim imageInBytes As Byte() = rdrDCS(1)
                Dim memoryStream As System.IO.MemoryStream = New System.IO.MemoryStream(imageInBytes, False)
                Dim image As System.Drawing.Image = System.Drawing.Image.FromStream(memoryStream)
                image.Save(TempPath & rdrDCS(0))
            End While
            ToProcess = True
        End If
        rdrDCS.Close()
    Catch ex As Exception
        ToProcess = False
        MessageBox.Show("Error accessing to the files: " & ex.Message)
    Finally
        conDCS.Close()
    End Try

我得到：“参数无效”在这一行：

Dim image As System.Drawing.Image = System.Drawing.Image.FromStream(memoryStream)

我已经明白这个错误与无效的图像数据有关，但我无法弄清楚可能是什么问题。

imageInBytes的长度为41473.数组中的某些项目的值为零。

这里可能有什么问题，或者也许，任何人都可以提供有效的代码来实现这个目标吗？

Answer 1

我们使用常用方法将文件从数据库字段保存到文件：

Public Function FieldToFile(ByVal sFileName As String, ByVal theField As Object) As Boolean
    ' Exceptions are handled by the caller

    If theField IsNot DBNull.Value Then
        Using oStream As New System.IO.FileStream(sFileName, IO.FileMode.Create, IO.FileAccess.Write)
            If oStream IsNot Nothing Then
                Dim aBytes As Byte()

                aBytes = DirectCast(theField, Byte())

                oStream.Write(aBytes, 0, aBytes.Length)
                oStream.Close()
            End If
        End Using
    End If

    Return True
End Function

可以这样调用：

Call FieldToFile(someFileName, rdrDCS(1)

使用vb.net检索存储在sql server中的excel文件

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