C# 如何从SQL Server中选择数据并将其保存到我的计算机

我从数据库中按名称选择了二进制数据，然后我显示了一个

SaveFileDialog

，将二进制数据保存在我计算机上的某个位置。 我写了下面的代码来实现这一点，但是当我打开保存的文件时，文件中没有任何数据。它只适用于txt文件。我怎样才能解决这个问题

 private void btnUpload_Click(object sender, EventArgs e)
    {
        fdTransfer.ShowDialog();
        string filePath = fdTransfer.FileName;
        string fileName=Path.GetFileName(filePath);
        string Ext=Path.GetExtension(fileName);
        string contentType = string.Empty;
        switch (Ext)
        {
            case ".doc":
                contentType = "application/vnd.ms-word";
                break;
            case ".docx":
                contentType = "application/vnd.ms-word";
                break;
            case ".txt":
                contentType = "application/vnd.ms-txt";
                break;
            case ".xls":
                contentType = "application/vnd.ms-excel";
                break;
            case ".xlsx":
                contentType = "application/vnd.ms-excel";
                break;
            case ".jpg":
                contentType = "image/jpg";
                break;
            case ".png":
                contentType = "image/png";
                break;
            case ".gif":
                contentType = "image/gif";
                break;
            case ".pdf":
                contentType = "application/pdf";
                break;
        }
        if (contentType != String.Empty)
        {

            Byte[] bytes = System.IO.File.ReadAllBytes(filePath);             
            SqlCommand cmd = new SqlCommand("InsertFile",Conn);
            Conn.Open();
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.Add("@FileName", SqlDbType.VarChar).Value = fileName;
            cmd.Parameters.Add("@ContentType", SqlDbType.VarChar).Value = contentType;
            cmd.Parameters.Add("@Content", SqlDbType.Binary).Value = bytes;
            int record = cmd.ExecuteNonQuery();
            lblMessage.ForeColor = System.Drawing.Color.Green;
            lblMessage.Text = "File Uploaded Successfully";
            Conn.Close();
        }
        else
        {
            lblMessage.ForeColor = System.Drawing.Color.Red;
            lblMessage.Text = "File format not recognised." +
              " Upload Image/Word/PDF/Excel formats";
        }
    }

   private void btnDownload_Click(object sender, EventArgs e)
    {
         try
        {
                   using (SqlCommand cmd = new SqlCommand("SelectFile", Conn))
                {
                    cmd.CommandType = CommandType.StoredProcedure;
                    Conn.Open();
                    cmd.Parameters.Add("@FileName", SqlDbType.VarChar).Value = fileName;                        string Ext = Path.GetExtension(fileName);
                    SqlDataReader sdr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                    if (sdr.HasRows)
                    {
                        sdr.Read();
                        byte[] content = sdr["Content"] as byte[];
                        if (fdDownload.ShowDialog() == DialogResult.OK)
                        {
                            FileStream fs = new FileStream(fdDownload.FileName + Ext
                          , FileMode.CreateNew, FileAccess.Write);
                        fs.Write(content, 0, content.Length);
                        fs.Flush();
                        fs.Close();
                        }
                    }
                }
                   lblMessage.ForeColor = System.Drawing.Color.Green;
                   lblMessage.Text = "File Downloaded Successfully";
                   Conn.Close();

        }
        catch (SqlException sqlEx)
        {
            lblMessage.ForeColor = System.Drawing.Color.Red;
            lblMessage.Text = "File not  Downloaded Successfully";
        }

    }

---

你能试试这样的吗？将数据转换为字节[]，然后将其写入文件

SqlDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection);
if (reader.HasRows)
{
reader.Read();
byte[] content = reader["FileContent"] as byte[];
FileStream fs = new FileStream(@"c:\temp\tempfile.txt"
  , FileMode.CreateNew, FileAccess.Write);
fs.Write(content, 0, content.Length);
fs.Flush();
fs.Close();
}

---

您确定

sdr[“Content”]

包含数据吗？您也从不关闭/刷新流。是的，在我的表的内容列中有。我应该在哪里关闭流？我编写了sw.close（），但当我打开保存的文件时，出现错误：无法打开文件，因为内容存在问题

SqlDataRaeader

和

StreamWriter

是否关闭？请对

SqlCommand

和

SqlDataReader

和

StreamWriter

使用

using

语句。如果您在数据库中存储二进制数据，而不是传递二进制参数而不是varchar，请将sqlDatatype.binary设为sqlDatatype并查看它是否工作。当我打开保存的文件时，也有同样的错误内容字节数组的大小是多少？您试图打开的文件类型是什么？为了测试，我定义了二进制（1000），然后上传并下载了一个具有2个字符二进制（1000）的docx-我怀疑您是否能将docx文件放入1000字节。