Oggetti LOB Oracle
Il provider di dati .NET Framework per Oracle include la classe OracleLob, usata per i tipi di dati LOB Oracle.
Un OracleLob può corrispondere a uno dei seguenti tipi di dati OracleType:
| Tipo di dati | Descrizione |
|---|---|
| BLOB | Tipo di dati BLOB Oracle in cui sono presenti dati binari per una dimensione massima di 4 GB. Esegue il mapping a un oggetto Array di tipo Byte. |
| Clob | Tipo di dati CLOB Oracle in cui sono presenti dati di tipo carattere, basati sul set di caratteri predefinito sul server, per una dimensione massima di 4 GB. Esegue il mapping a String. |
| NClob | Tipo di dati NCLOB Oracle in cui sono presenti dati di tipo carattere, basati sul set di caratteri nazionale sul server, per una dimensione massima di 4 GB. Esegue il mapping a String. |
Un OracleLob si differenzia da un tipo OracleBFile in quanto i dati sono memorizzati sul server anziché su un file fisico nel sistema operativo. Contrariamente all'oggetto OracleBFile, che è sempre di sola lettura, può trattarsi di un oggetto di lettura-scrittura.
Creazione, recupero e scrittura di un LOB
Nell'esempio in C# seguente viene illustrato come creare LOB in una tabella Oracle, quindi come recuperarli e scriverli sotto forma di oggetti OracleLob. L'esempio mostra come usare l'oggetto OracleDataReader e i metodi OracleLobRead e Write. Vengono usati i tipi di dati Oracle BLOB, CLOB e NCLOB.
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 manipulate 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();
}
}
Creazione di un LOB temporaneo
Nell'esempio C# seguente viene illustrato come creare un LOB temporaneo.
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();