• Microsoft’s .NET data provider for ODBC (or ODBC.NET)
• Microsoft’s .NET data provider for OLEDB (or OLEDB.NET)
• Microsoft’s .NET data provider for Oracle
• Oracle’s data provider for .NET (or ODP.NET)

There are several ways to connect to Oracle database from within .NET. Each of those methods having its own advantages and disadvantages. But in this post we concentrate only on how to connect to Oracle database from .Net. It is necessary to have Oracle 8i, 9i or Oracle 10g client installed on your system.

Proper Connection descriptors are to be configured on your system to connect to Oracle. The connection descriptors for oracle lies in the file called TNSNAMES.ORA . TNS stands for Transparent Network Substrate. You can locate the tnsname.ora file in your system at the Path <oracle_home>/network/admin/tnsname.ora. If it is already configured and you are able to connect to Oracle 9i database thru SQL* PLUS , then there is no need to disturb this file.
An example of connection descriptor in my system is

XE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = LENOVO)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = XE)
    )
  )

I have installed Oracle 10g Express edition on my system.The above configuration script shows that the Oracle database server is available at 127.0.0.1 (local host) and listening at port 1521.The service name (or SID) to connect to the server is xe. The whole description is assigned to a name XE.

Connecting to Oracle Using .NET Data Provider for OLEDB
This method is mostly preferred when you are trying to develop database-independent applications based on ADO.NET 1.1.
The following code can be used to connect to Oracle database using .Net provider for OLEDB.

Imports System.Data
Imports System.Data.OleDb
Public Class Oracle_conn
Private Sub btnConn_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btnConn.Click
Dim conn As New OleDbConnection
conn.ConnectionString = "Provider=msdaora;Data Source=xe;User Id=strinix;Password=xxxx;"

Try
  'Catch an error when connecting to Oracle
   conn.Open()
  'close the connection before exiting
  conn.Close()
  MessageBox.Show("Connected to Oracle")
Catch ex As Exception
'If connection failed display an error
MessageBox.Show("Unable to connect. " & ex.Message)
End Try
End Sub
End Class

 System.Data.OleDb is the namespace used to deal .NET Data Provider for OLEDB.When we are working with OLEDB data sources, we need to connect through the OleDbConnection class. The connection string information would also be different when we deal with .NET Data Provider for OLEDB to connect to Oracle.

Connecting to Oracle database Using .NET Data Provider for ODBC

ODBC is the slowest among all the data connector used to connect oracle. This method is used when you are trying to develop multi-platform database independent applications using ADO.NET. This method is preferable, if you want to connect to legacy systems or database systems existing on other platforms.
The following is the code to connect to Oracle database using .NET data provider for ODBC:

Imports System.Data
Imports System.Data.odbc
Public Class Oracle_conn
Private Sub btnConn_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btnConn.Click
Dim conn As New OdbcConnection
conn.ConnectionString = "Driver={Microsoft ODBC for Oracle};Server=xe;Uid=strinix;Pwd=xxxxx;"
Try
  'Catch an error when connecting to Oracle
   conn.Open()
  'close the connection before exiting
   conn.Close()
MessageBox.Show("Connected to Oracle")
Catch ex As Exception
'If connection failed display an error
MessageBox.Show("Unable to connect. " & ex.Message)
End Try
End Sub
End Class

System.Data.odbc namespace is used to deal with .NET Data Provider for ODBC. System.Data.OleDb is the namespace used for Oledb Connection. When we are working with ODBC data sources, we need to connect through the OdbcConnection class.

Connecting to Oracle using Microsoft’s .NET Data Provider for Oracle

Microsoft has finally extended its support for Oracle database in visual studio by Providing  an exclusive .Net data provider for Oracle. Microsoft has developed this driver inorder to make use of advanced and extensive features available in Oracle which were not supported by oledb and Odbc. This is the most preferred method used by Microsoft developers to connect and explore Oracle.
Before using this data Provider you need to add a reference to the assembly System.Data.OracleClient as show in below picture:

You can use the following code to connect to Oracle after making a reference
Imports System.Data.OracleClient

Public Class Oracle_conn
Private Sub btnConn_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btnConn.Click
Dim conn As New OracleConnection
conn.ConnectionString = "Data Source=xe; User Id=scott;Password=tiger;"Try
   'try connecting to oracle
    conn.Open()
  'close the connection before exiting
   conn.Close()
MessageBox.Show("Connected to Oracle")
Catch ex As Exception
'If connection failed display an error
MessageBox.Show("Unable to connect. " & ex.Message)
End Try
End Sub
End Class

Connecting Using Oracle Data Provider for .NET (ODP.NET)
This data provider is developed by Oracle to facilitate developers connecting to Oracle databases with tight integration (along with best performance) and advanced features. This method is the best even when you are trying to access Oracle, as ODP.NET has tight integration with Oracle database. To use this method you need to download ODP.NET from web and install on your system. As specified previously you need add a reference to this assembly from visual studio as shown in the picture below:

Once  a reference has been added , you can proceed with the following code to connect to Oracle database using ODP.NET

Imports oracle.DataAccess.Client
Public Class Oracle_conn
Private Sub btnConn_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btnConn.Click
Dim conn As New OracleConnection
conn.ConnectionString = "Data Source=xe;User Id=scott;Password=tiger;"
Try
   'try connecting to oracle
    conn.Open()
  'close the connection before exiting
   conn.Close()
MessageBox.Show("Connected to Oracle")
Catch ex As Exception
'If connection failed display an error
MessageBox.Show("Unable to connect. " & ex.Message)
End Try
End Sub
End Class