从SQL Server数据库检索文件

问题描述

我正在建立一个站点，在该站点中必须使用文件上载控制来附加支持日志/邮件等.我认为将文件保存在数据库中将是更好的选择.

I am building a site where I have to use file upload control for attaching support logs / mails etc... I felt that saving files in a database would be the better option.

我正在使用下面的代码上传文件.但是，我无法测试它，因为我不知道如何从数据库中检索文件.有人可以帮我吗?

I am using the code below to upload files. However, I am not able to test it as I don't know how to retrieve files from a database. Can some one please help me on this?

文件类型可以是任何类型.

File type can be anything.

代码:

FileUrl = "C:\\Attachments\\"+Path.GetFileName(UploadCtrl.NavigateUrl);
FileStream fs = new FileStream(FileUrl, FileMode.Open, FileAccess.Read);
BinaryReader br = new BinaryReader(fs);
long numBytes = new FileInfo(FileUrl).Length;
buff = br.ReadBytes(Convert.ToInt32(numBytes));
SqlConnection conn = new SqlConnection(SQLSrc.ConnectionString);
conn.Open();
SqlCommand command = conn.CreateCommand();
string InsertQueryText = "insert into Attachments values ('" + Path.GetFileName(FileUrl) + "','" + MIME(Path.GetExtension(Att_Overview_Link.NavigateUrl)) + "','" + buff + "');";
command.CommandText = InsertQueryText;
command.ExecuteNonQuery();

在这里，MIME是用户定义的函数，用于获取指定文件类型的MIME值.

Here, MIME is the user defined function to get the MIME value of the specified file type.

前端:C#ASP.NET和SQL Server作为后端

Frontend: C# ASP.NET and SQL Server as backend

推荐答案

首先修复您的代码以删除 SQL注入漏洞:

Start by fixing your code to remove the SQL Injection vulnerability:

FileUrl = "C:\\Attachments\\" + Path.GetFileName(UploadCtrl.NavigateUrl);

using (SqlConnection conn = new SqlConnection(SQLSrc.ConnectionString))
using (SqlCommand command = conn.CreateCommand())
{
   command.CommandText = "insert into Attachments values (@FileName, @MimeType, @FileBytes)";
   command.Parameters.AddWithValue("@FileName", Path.GetFileName(FileUrl));
   command.Parameters.AddWithValue("@MimeType", MIME(Path.GetExtension(Att_Overview_Link.NavigateUrl)));
   command.Parameters.AddWithValue("@FileBytes", File.ReadAllBytes(FileUrl));

   conn.Open();
   command.ExecuteNonQuery();
}

注意::我不确定您的UploadCtrl是什么，但是大多数文件上载控件都可以作为Stream而不是服务器上的文件名来直接访问上载的文件.根据此特定控件的工作方式，您可能需要更改读取上传文件的方式.

NB: I'm not sure what your UploadCtrl is, but most file upload controls provide direct access to the uploaded file as a Stream, not a file name on the server. Depending on how this specific control works, you might need to change how you read the uploaded file.

要检索文件，您将选择相关的名称，MIME类型和字节，然后将它们写入响应:

To retrieve the file, you would select the relevant name, MIME type and bytes, and write them to the response:

using (SqlConnection conn = new SqlConnection(SQLSrc.ConnectionString))
using (SqlCommand command = conn.CreateCommand())
{
   command.CommandText = "SELECT FileName, MimeType, FileBytes FROM Attachments WHERE PK = @PK";
   command.Parameters.AddWithValue("@PK", Request.QueryString["pk"]);

   conn.Open();
   using (SqlDataReader reader = command.ExecuteReader(CommandBehavior.SequentialAccess | CommandBehavior.CloseConnection))
   {
      if (reader.Read())
      {
         string name = reader.GetString(reader.GetOrdinal("FileName"));
         Response.AppendHeader("Content-Disposition", "attachment; filename=" + name);
         Response.ContentType = reader.GetString(reader.GetOrdinal("MimeType"));

         int startIndex = 0;
         byte[] buffer = new byte[4096];
         int fieldIndex = reader.GetOrdinal("FileBytes");
         int bytesRead = (int)reader.GetBytes(fieldIndex, startIndex, buffer, 0, buffer.Length);
         while (bytesRead != 0)
         {
            Response.OutputStream.Write(buffer, 0, bytesRead);
            Response.Flush();

            startIndex += bytesRead;
            bytesRead = (int)reader.GetBytes(fieldIndex, startIndex, buffer, 0, buffer.Length);
         }
      }
   }
}

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