下载大文件，保存在数据库中

本文介绍了下载大文件，保存在数据库中的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我们有很多文件，在我们的SQL Server数据库中保存为二进制文件。 我已经将一个.ashx文件传递给用户。 不幸的是，当文件变得相当大时，它将失败，并出现以下错误：

We have a lot of files, saved as binary in our SQL Server database. I have made an .ashx file, that delivers these files, to the users. Unfortunately, when the files become rather large, it will fail, with the following error:

算术中溢出或下溢操作

Overflow or underflow in the arithmetic operation

我假设它的内存不足，因为我将二进制文件加载到一个字节[]。

I assume it runs out of memory, as I load the binary into a byte[].

所以，我的问题是，如何做这个功能，读取大块（也许？），当它是从数据库表？它也似乎是Response.TransmitFile（）是一个很好的选择，但是再次，这将如何与数据库工作？

So, my question is, how can I make this functionality, read in chunks (maybe?), when it is from a database table? It also seems like Response.TransmitFile() is a good option, but again, how would this work with a database?

DB.GetReposFile（），在代码在下面，从数据库获取文件。有各种字段，条目为：文件名，ContentType，datestamps和FileContent为varbinary。

The DB.GetReposFile(), in the code beneath, gets the file from the database. There are various fields, for the entry: Filename, ContentType, datestamps and the FileContent as varbinary.

这是我的功能，提供文件： / p>

This is my function, to deliver the file:

context.Response.Clear(); try { if (!String.IsNullOrEmpty(context.Request.QueryString["id"])) { int id = Int32.Parse(context.Request.QueryString["id"]); DataTable dtbl = DB.GetReposFile(id); string FileName = dtbl.Rows[0]["FileName"].ToString(); string Extension = FileName.Substring(FileName.LastIndexOf('.')).ToLower(); context.Response.ContentType = ReturnExtension(Extension); context.Response.AddHeader("Content-Disposition", "attachment; filename=" + FileName); byte[] buffer = (byte[])dtbl.Rows[0]["FileContent"]; context.Response.OutputStream.Write(buffer, 0, buffer.Length); } else { context.Response.ContentType = "text/html"; context.Response.Write("<p>Need a valid id</p>"); } } catch (Exception ex) { context.Response.ContentType = "text/html"; context.Response.Write("<p>" + ex.ToString() + "</p>"); }

更新： 函数I结束了，是下面列出的。 DB.GetReposFileSize（）只是获取内容Datalength，正如蒂姆提到的。 我在原始代码中调用这个函数，而不是这两行：

Update: The function I ended up with, is the one listed below. DB.GetReposFileSize() simply gets the content Datalength, as Tim mentions. I call this function, in the original code, instead of these two lines:

byte[] buffer = (byte[])dtbl.Rows[0]["FileContent"]; context.Response.OutputStream.Write(buffer, 0, buffer.Length);

新的下载功能：

private void GetFileInChunks(HttpContext context, int ID) { //string path = @"c:\somefile.txt"; //FileInfo file = new FileInfo(path); int len = DB.GetReposFileSize(ID); context.Response.AppendHeader("content-length", len.ToString()); context.Response.Buffer = false; //Stream outStream = (Stream)context.Response.OutputStream; SqlConnection conn = null; string strSQL = "select FileContent from LM_FileUploads where ID=@ID"; try { DB.OpenDB(ref conn, DB.DatabaseConnection.PDM); SqlCommand cmd = new SqlCommand(strSQL, conn); cmd.Parameters.AddWithValue("@ID", ID); SqlDataReader reader = cmd.ExecuteReader(CommandBehavior.SequentialAccess); reader.Read(); byte[] buffer = new byte[1024]; int bytes; long offset = 0; while ((bytes = (int)reader.GetBytes(0, offset, buffer, 0, buffer.Length)) > 0) { // TODO: do something with `bytes` bytes from `buffer` context.Response.OutputStream.Write(buffer, 0, buffer.Length); offset += bytes; } } catch (Exception ex) { throw ex; } finally { DB.CloseDB(ref conn); } }

推荐答案

你可以使用 DATALENGTH 获取 VARBINARY 的大小，并使用 SqldataReader 将其流式传输，它的 阅读 - 或 ReadBytes -Method。

You can use DATALENGTH to get the size of the VARBINARY and stream it for instance with a SqldataReader and it's Read-or ReadBytes-Method.

看看这个答案看看一个实现：在ASP.NET中流式传输文件的最佳方式

Have a look at this answer to see an implementation: Best way to stream files in ASP.NET