Oracle LOB

更新：November 2007

Oracle .NET Framework 数据提供程序包括 OracleLob 类，该类用于使用 Oracle LOB 数据类型。

OracleLob 可能是下列 OracleType 数据类型之一：

OracleLob 与 OracleBFile 的区别在于前者的数据存储在服务器上而不是存储在操作系统的物理文件中。 它也可以是一个读写对象，这一点与 OracleBFile 不同（后者始终为只读）。

创建、检索和写入 LOB

以下 C# 示例演示如何在 Oracle 表中创建 LOB，然后以 OracleLob 对象的形式检索并写入。 该示例演示如何使用 OracleDataReader 对象以及 OracleLobRead 和 Write 方法。 该示例使用 Oracle BLOB、CLOB 和 NCLOB 数据类型。

[C#]

using System;
using System.IO;            
using System.Text;           
using System.Data;            
using System.Data.OracleClient;

// LobExample
public class LobExample
{
   public static int Main(string[] args)
   {
      //Create a connection.
      OracleConnection conn = new OracleConnection(
         "Data Source=Oracle8i;Integrated Security=yes");
      using(conn)
      {
         //Open a connection.
         conn.Open();
         OracleCommand cmd = conn.CreateCommand();

         //Create the table and schema.
         CreateTable(cmd);

         //Read example.
         ReadLobExample(cmd);

         //Write example
         WriteLobExample(cmd);
      }

      return 1;
   }

   // ReadLobExample
   public static void ReadLobExample(OracleCommand cmd)
   {
      int actual = 0;

      // Table Schema:
      // "CREATE TABLE tablewithlobs (a int, b BLOB, c CLOB, d NCLOB)";
      // "INSERT INTO tablewithlobs values (1, 'AA', 'AAA', N'AAAA')";
      // Select some data.
      cmd.CommandText = "SELECT * FROM tablewithlobs";
      OracleDataReader reader = cmd.ExecuteReader();
      using(reader)
      {
         //Obtain the first row of data.
         reader.Read();
         
         //Obtain the LOBs (all 3 varieties).
         OracleLob blob = reader.GetOracleLob(1);
         OracleLob clob = reader.GetOracleLob(2);
         OracleLob nclob = reader.GetOracleLob(3);

         //Example - Reading binary data (in chunks).
         byte[] buffer = new byte[100];
         while((actual = blob.Read(buffer, 0, buffer.Length)) >0)
            Console.WriteLine(blob.LobType + ".Read(" + buffer + ", " + 
              buffer.Length + ") => " + actual);

         // Example - Reading CLOB/NCLOB data (in chunks).
         // Note: You can read character data as raw Unicode bytes 
         // (using OracleLob.Read as in the above example).
         // However, because the OracleLob object inherits directly 
         // from the .Net stream object, 
         // all the existing classes that manipluate streams can 
         // also be used. For example, the 
         // .Net StreamReader makes it easier to convert the raw bytes 
         // into actual characters.
         StreamReader streamreader = 
           new StreamReader(clob, Encoding.Unicode);
         char[] cbuffer = new char[100];
         while((actual = streamreader.Read(cbuffer, 
           0, cbuffer.Length)) >0)
            Console.WriteLine(clob.LobType + ".Read(
              " + new string(cbuffer, 0, actual) + ", " + 
              cbuffer.Length + ") => " + actual);

         // Example - Reading data (all at once).
         // You could use StreamReader.ReadToEnd to obtain 
         // all the string data, or simply
         // call OracleLob.Value to obtain a contiguous allocation 
         // of all the data.
         Console.WriteLine(nclob.LobType + ".Value => " + nclob.Value);
      }
   }

   // WriteLobExample
   public static void WriteLobExample(OracleCommand cmd)
   {
      //Note: Updating LOB data requires a transaction.
      cmd.Transaction = cmd.Connection.BeginTransaction();
      
      // Select some data.
      // Table Schema:
      // "CREATE TABLE tablewithlobs (a int, b BLOB, c CLOB, d NCLOB)";
      // "INSERT INTO tablewithlobs values (1, 'AA', 'AAA', N'AAAA')";
      cmd.CommandText = "SELECT * FROM tablewithlobs FOR UPDATE";
      OracleDataReader reader = cmd.ExecuteReader();
      using(reader)
      {
         // Obtain the first row of data.
         reader.Read();

         // Obtain a LOB.
         OracleLob blob = reader.GetOracleLob(1/*0:based ordinal*/);

         // Perform any desired operations on the LOB 
         // (read, position, and so on).

         // Example - Writing binary data (directly to the backend).
         // To write, you can use any of the stream classes, or write
         // raw binary data using 
         // the OracleLob write method. Writing character vs. binary 
         // is the same;
         // however note that character is always in terms of 
         // Unicode byte counts
         // (for example, even number of bytes - 2 bytes for every
         // Unicode character).
         byte[] buffer = new byte[100];
         buffer[0] = 0xCC;
         buffer[1] = 0xDD;
         blob.Write(buffer, 0, 2);
         blob.Position = 0;
         Console.WriteLine(blob.LobType + ".Write(
           " + buffer + ", 0, 2) => " + blob.Value);
         
         // Example - Obtaining a temp LOB and copying data 
         // into it from another LOB.
         OracleLob templob = CreateTempLob(cmd, blob.LobType);
         long actual = blob.CopyTo(templob);
         Console.WriteLine(blob.LobType + ".CopyTo(
            " + templob.Value + ") => " + actual);

         // Commit the transaction now that everything succeeded.
         // Note: On error, Transaction.Dispose is called 
         // (from the using statement)
         // and will automatically roll back the pending transaction.
         cmd.Transaction.Commit();
      }
   }

   // CreateTempLob
   public static OracleLob CreateTempLob(
     OracleCommand cmd, OracleType lobtype)
   {
      //Oracle server syntax to obtain a temporary LOB.
      cmd.CommandText = "DECLARE A " + lobtype + "; "+
                     "BEGIN "+
                        "DBMS_LOB.CREATETEMPORARY(A, FALSE); "+
                        ":LOC := A; "+
                     "END;";
      
      //Bind the LOB as an output parameter.
      OracleParameter p = cmd.Parameters.Add("LOC", lobtype);
      p.Direction = ParameterDirection.Output;

      //Execute (to receive the output temporary LOB).
      cmd.ExecuteNonQuery();

      //Return the temporary LOB.
      return (OracleLob)p.Value;
   }

   // CreateTable
   public static void CreateTable(OracleCommand cmd)
   {
      // Table Schema:
      // "CREATE TABLE tablewithlobs (a int, b BLOB, c CLOB, d NCLOB)";
      // "INSERT INTO tablewithlobs VALUES (1, 'AA', 'AAA', N'AAAA')";
      try
      {
         cmd.CommandText   = "DROP TABLE tablewithlobs";
         cmd.ExecuteNonQuery();
      }
      catch(Exception)
      {
      }
      
      cmd.CommandText = 
        "CREATE TABLE tablewithlobs (a int, b BLOB, c CLOB, d NCLOB)";
      cmd.ExecuteNonQuery();
      cmd.CommandText = 
        "INSERT INTO tablewithlobs VALUES (1, 'AA', 'AAA', N'AAAA')";
      cmd.ExecuteNonQuery();
   }
}

创建临时 LOB

以下 C# 示例演示如何创建临时 LOB。

[C#]

OracleConnection conn = new OracleConnection(
  "server=test8172; integrated security=yes;");
conn.Open();

OracleTransaction tx = conn.BeginTransaction();

OracleCommand cmd = conn.CreateCommand();
cmd.Transaction = tx;
cmd.CommandText = 
  "declare xx blob; begin dbms_lob.createtemporary(
  xx, false, 0); :tempblob := xx; end;";
cmd.Parameters.Add(new OracleParameter("tempblob",
  OracleType.Blob)).Direction = ParameterDirection.Output;
cmd.ExecuteNonQuery();
OracleLob tempLob = (OracleLob)cmd.Parameters[0].Value;
tempLob.BeginBatch(OracleLobOpenMode.ReadWrite);
tempLob.Write(tempbuff,0,tempbuff.Length);
tempLob.EndBatch();
cmd.Parameters.Clear();
cmd.CommandText = "myTable.myProc";
cmd.CommandType = CommandType.StoredProcedure;  
cmd.Parameters.Add(new OracleParameter(
  "ImportDoc", OracleType.Blob)).Value = tempLob;
cmd.ExecuteNonQuery();

tx.Commit();

请参见

其他资源

Oracle 和 ADO.NET