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
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下载大文件,保存在数据库中
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