Oracle中Clob与Blob字段的读取

Oracle中若以字符串的形式写入数据到Clob字段中，默认的长度为4000，最大可存储4G。

     直接将字符串写入Clob字段中，则最大可写4000个字节；若要写入大的字符数据，可以将字符数据以二进制流的形式写入。

写入Clob(Blob代码):

OracleConnection conn = new OracleConnection(GetConfigUserConnectionString());
            conn.Open();
            OracleTransaction tran = conn.BeginTransaction();
            string id = string.Empty;
            OracleCommand command = null;
            try
            {
                command = new OracleCommand();
                command.Connection = conn;
                double scale = 0;
                if (ct.Scale.IndexOf(":") == -1)
                {
                    scale = BasicOperate.GetDouble(ct.Scale, true);
                }
                else
                {
                    scale = BasicOperate.GetDouble(ct.Scale.Substring(ct.Scale.IndexOf(":") + 1), true);
                }

//在插入时先存一个空的empty_clob()[empty_blob()]
                command.CommandText = string.Format(@"insert into chart(chartname,charttype,source,scale,producttime,"
                    +"xml_definition) values('{0}','{1}','{2}',{3},'{4}',empty_clob()) "
                    +"returning chartid into :rid",
                     ct.ChartName, ct.ChartType, ct.Source, scale, ct.ProductTime, ct.xmlDefinition);
                command.Parameters.Add("rid", OracleDbType.Varchar2, 32).Direction = ParameterDirection.Output;
                command.ExecuteNonQuery();
                id = command.Parameters["rid"].Value.ToString();

//读入clob字段进行编辑
                command.CommandText = string.Format("select xml_definition from chart where chartid='{0}' for update", id);
                using (OracleDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        OracleClob clob = reader.GetOracleClob(0);//读入二进制对性
                        clob.Erase();//清空其中的数据
                        clob.Position = 0;
                        clob.BeginChunkWrite();//开始写入
                        int buffersize = 100;
                        int retval = 0;
                        byte[] bts = new byte[buffersize];

//将字符串序列化为二进制流
                        MemoryStream stream = new MemoryStream();
                        BinaryFormatter formatter = new BinaryFormatter();
                        formatter.Serialize(stream, ct.xmlDefinition);

//将二进制流写入Clob字符中
                        stream.Seek(0, SeekOrigin.Begin);
                        retval = stream.Read(bts, 0, buffersize);
                        while (retval == buffersize)
                        {
                            clob.Write(bts, 0, buffersize);
                            retval = stream.Read(bts, 0, buffersize);
                        }
                            clob.Write(bts, 0, 100);
                        clob.EndChunkWrite();//结束写入
                        clob.Flush();//刷新
                        clob.Close();//关闭 
                    }
                    reader.Close();
                }
                tran.Commit();
            }
            catch (Exception ex)
            {
                tran.Rollback();
                //throw new Exception(ex.Message);
            }
            finally
            {
                if (conn.State == ConnectionState.Open)
                {
                    conn.Close();
                }
            }

 

 

读取Clob(blob)字段:

 

。。。 

 using (OracleDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        OracleClob clob = reader.GetOracleClob(0);//读取二进制字段
                        clob.Position = 0;//指向起点
                        byte[] tt = new byte[clob.Length];
                        clob.Read(tt, 0, (int)clob.Length);//将Clob读为二进制数据
                        MemoryStream ms = new MemoryStream(tt);
                        BinaryFormatter bb = new BinaryFormatter();
                        object oo = bb.Deserialize(ms);//反序列化取出字符数据

                    }}