Tài liệu Reading and Writing Binary Data with Oracle pdf

[ Team LiB ]Recipe 9.12 Reading and Writing Binary Data with Oracle Problem You need to read and write binary data from and to an Oracle database.. An Oracle DataAdapter is created and

[ Team LiB ]

Recipe 9.12 Reading and Writing Binary Data with Oracle

Problem

You need to read and write binary data from and to an Oracle database

Solution

Use the techniques shown in the following example

The sample code contains two event handlers:

Read Button.Click

Clears the controls on the form and builds a SQL statement to get the record for the specified ID from the Oracle table TBL0912 A connection is created and a command is built using the SQL statement and executed to build a DataReader The BLOB is retrieved from the DataReader and displayed in the PictureBox on the form The CLOB and NCLOB values are retrieved from the DataReader and displayed in text boxes on the form

Write Button.Click

Gets the ID from the TextBox on the form A BLOB is retrieved from a user-specified file and loaded into a Byte array An Oracle DataAdapter is created and a new table is created using the FillSchema( ) command A CommandBuilder is created from the DataAdapter A new row is created where the BLOB value is set from the file specified by the user and the CLOB, and NCLOB values are set from the text boxes on the form The new row is added to the table and the data updated back to the source

The C# code is shown in Example 9-15

Example 9-15 File: ReadWriteBinaryDataFromOracleForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Drawing;

using System.Windows.Forms;

using System.Text;

using System.IO;

using System.Data;

using System.Data.OracleClient;

private OpenFileDialog ofd;

private const String TABLENAME = "TBL0912";

private const String ID_FIELD = "ID";

private const String BLOBFIELD_FIELD = "BLOBFIELD";

private const String CLOBFIELD_FIELD = "CLOBFIELD";

private const String NCLOBFIELD_FIELD = "NCLOBFIELD";

//

private void readButton_Click(object sender, System.EventArgs e)

{

// Clear the controls

blobPictureBox.Image = null;

clobTextBox.Clear( );

nclobTextBox.Clear( );

String sqlText = "SELECT * FROM " + TABLENAME + " WHERE ID = " + idTextBox.Text;

// Create the connection and command

OracleConnection conn = new OracleConnection(

ConfigurationSettings.AppSettings["Oracle_ConnectString"]);

OracleCommand cmd = new OracleCommand(sqlText, conn);

conn.Open( );

// Create the DataReader

OracleDataReader dr = cmd.ExecuteReader( );

// Iterate over the collection of rows in the DataReader

if(dr.Read( ))

{

// Retrieve the BLOB into a stream

Byte[] blob = null;

if(!dr.IsDBNull(1))

blob = (Byte[])dr.GetOracleLob(1).Value;

MemoryStream ms = new MemoryStream(blob);

// Display the BLOB in the PictureBox

blobPictureBox.Image = Image.FromStream(ms);

ms.Close( );

// Get the CLOB

if(!dr.IsDBNull(2))

clobTextBox.Text = dr.GetOracleLob(2).Value.ToString( );

// Get the NCLOB

if(!dr.IsDBNull(3))

nclobTextBox.Text = dr.GetOracleLob(3).Value.ToString( ); }

else

{

MessageBox.Show("No record found.", "Access Oracle LOB Data", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);

}

dr.Close( );

conn.Close( );

}

private void writeButton_Click(object sender, System.EventArgs e) {

// Get the user-supplied ID

int id;

try

{

id = Convert.ToInt32(idTextBox.Text);

}

catch(System.Exception ex)

{

MessageBox.Show(ex.Message, "Access Oracle LOB Data",

MessageBoxButtons.OK, MessageBoxIcon.Exclamation);

return;

}

// Save the BLOB, CLOB, and NCLOB

if (ofd.ShowDialog( ) == DialogResult.OK)

{

// Get a BLOB from a user-specified file

FileStream fs = new FileStream(ofd.FileName,

FileMode.OpenOrCreate, FileAccess.Read);

Byte[] blob = new Byte[fs.Length];

fs.Read(blob, 0, blob.Length);

fs.Close( );

// Create a DataAdapter and table

OracleDataAdapter da = new OracleDataAdapter("SELECT * FROM " + TABLENAME,

ConfigurationSettings.AppSettings["Oracle_ConnectString"]);

DataTable table = new DataTable( );

// Just get the schema

da.FillSchema(table, SchemaType.Source);

OracleCommandBuilder cb = new OracleCommandBuilder(da);

// Create a row containing the new BLOB, CLOB, and NCLOB data DataRow row = table.NewRow( );

row[ID_FIELD] = id;

row[BLOBFIELD_FIELD] = blob;

if(clobTextBox.TextLength > 0)

row[CLOBFIELD_FIELD] = clobTextBox.Text;

if(nclobTextBox.TextLength > 0)

row[NCLOBFIELD_FIELD] = nclobTextBox.Text;

// Add the row to the table

table.Rows.Add(row);

// Update the Oracle database using the DataAdapter

try

{

da.Update(table);

}

catch(System.Exception ex)

{

MessageBox.Show(ex.Message, "Access Oracle LOB Data",

MessageBoxButtons.OK,

MessageBoxIcon.Exclamation);

return;

}

MessageBox.Show("Record successfully created.",

"Access Oracle LOB Data", MessageBoxButtons.OK,

MessageBoxIcon.Information);

}

}

Discussion

The GetOracleLob( ) typed accessor method of the OracleDataReader gets the value of the specified column as an OracleLob object representing a Large Object Binary (LOB) data type stored on an Oracle server An Oracle LOB can be one of three types as

described in Table 9-4

Table 9-4 Oracle LOB data type Data

Blob Oracle data type containing binary data with a maximum size of 4 GB This

data type maps to a Byte array

Clob Oracle data type containing character data based on the default character set

of the server with a maximum size of 4 GB This data type maps to a String NClob Oracle data type containing character data based on the national character set

of the server with a maximum size of 4 GB This data type maps to a String

The Oracle NET data provider handles CLOB and NCLOB data as Unicode Each character is therefore two bytes long

See Recipe 9.12 for a general discussion about reading and writing BLOB data from and

to a data source

[ Team LiB ]