odp.net 读写oracle blob字段

DEVELOPER: ODP.NET Serving Winning LOBs：

http://www.oracle.com/technetwork/issue-archive/2005/05-nov/o65odpnet-085139.html

Data Provider for .NET Developer's Guide：

https://docs.oracle.com/database/121/ODPNT/OracleBlobClass.htm#ODPNT4035

从blob字段读取一个图片文件的代码：

       OracleConnection con = new OracleConnection(connStr);
        con.Open();

        // statement to get a blob
        string sql = "select yz from sysusers where yhdh='123'";

        // create command object
        // InitialLOBFetchSize
        //  defaults to 0
        OracleCommand cmd = new OracleCommand(sql, con);

        // create a datareader
        using (OracleDataReader dr = cmd.ExecuteReader())
        {
            // read the single row result
            dr.Read();
            // use typed accessor to retrieve the blob
            OracleBlob blob = dr.GetOracleBlob(0);

            // create a memory stream from the blob
            using (MemoryStream ms = new MemoryStream(blob.Value))
            {
                // set the image property equal to a bitmap
                // created from the memory stream
                pictureBox1.Image = new Bitmap(ms);
            }
        }

保存文件到blob字段的代码：

        con.Open();

        // 利用事务处理（必须）
        OracleTransaction transaction = con.BeginTransaction();
        string sql="select yz from sysusers where yhdh='123' FOR UPDATE";
        OracleCommand cmd = new OracleCommand(sql, con);
        
        using ( OracleDataReader reader = cmd.ExecuteReader())
        {
            //Obtain the first row of data.
            reader.Read();
            //Obtain a LOB.
            OracleBlob blob = reader.GetOracleBlob(0);
            blob.Erase();
            // 将文件写入 BLOB 中
            byte[] Buffer;
            FileStream fs = new FileStream(@"d:1.jpg", FileMode.Open);
            using (MemoryStream ms = new MemoryStream())
            {
                int b;
                while ((b = fs.ReadByte()) != -1)
                {
                    ms.WriteByte((byte)b);
                }
                Buffer = ms.ToArray();
            }

            // Begin ChunkWrite to improve performance
            // Index updates occur only once after EndChunkWrite
            blob.Position=0;
            blob.BeginChunkWrite();  //启用BeginChunkWrite不是必须，只与性能有关
            blob.Write(Buffer, 0,Buffer .Length);  //从字节数据写入blob字段
            blob.EndChunkWrite();
            blob.Close();
        }
        // 提交事务
        transaction.Commit();
        con.Close();