在 C#/SQL 2005 中读取 BLOB 数据的内存有效方法

问题描述

使用 C# 3.5 读取 SQL 2005 图像字段最有效的内存方法是什么?

What's the most memory effective way to read an SQL 2005 image field using C# 3.5?

现在我有一个 (byte[])cm.ExecuteScalar("...").

如果我不能将所有字段内容读入内存，那就太好了.

If I could not read all field content into memory, that would be nice.

推荐答案

在此处查看这篇优秀的文章 或此博文详细说明如何操作.

See this excellent article here or this blog post for a long explanation how to do it.

基本上，您需要使用 SqlDataReader 并在创建它时为其指定 SequentialAccess - 然后您可以以最适合您的任何大小的块从数据库中读取(或写入)BLOB.

Basically, you need to use a SqlDataReader and specify SequentialAccess to it when you create it - then you can read (or write) the BLOB from the database in chunks of whatever size is best for you.

基本上是这样的:

SqlDataReader myReader = getEmp.ExecuteReader(CommandBehavior.SequentialAccess);

while (myReader.Read())
{
   int startIndex = 0;

   // Read the bytes into outbyte[] and retain the number of bytes returned.
   retval = myReader.GetBytes(1, startIndex, outbyte, 0, bufferSize);

   // Continue reading and writing while there are bytes beyond the size of the buffer.
   while (retval == bufferSize)
   {
      // write the buffer to the output, e.g. a file
      ....

      // Reposition the start index to the end of the last buffer and fill the buffer.
      startIndex += bufferSize;
      retval = myReader.GetBytes(1, startIndex, outbyte, 0, bufferSize);
   }

   // write the last buffer to the output, e.g. a file
   ....
}

// Close the reader and the connection.
myReader.Close();

马克

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