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Build a .NET Application on the Oracle Database with Visual Studio 2005 or 2008

By John Paul Cook, Published September 2008

Learn the basic yet essential processes involved in building a .NET application that uses an Oracle database.

With the popularity of Microsoft's .NET Framework, many developers are hungry for information about the best means of integrating .NET applications with Oracle—not only in terms of basic connectivity, but also in relationship to effective and efficient application development using Visual Studio 2005 or 2008.

In this article, I'll explain the basic yet essential processes involved in building a .NET application that uses an Oracle database, including:

  • How to add project references to support Oracle class libraries in your .NET project
  • How to create Oracle Database connection strings
  • How to work with Connection, Command, and DataReader objects

You will have the opportunity to apply what you have learned in three practice labs, ranging in difficulty from the relatively simple to the more complex. The article's screenshots are taken from Visual Studio 2008, but the experience is very similar in Visual Studio 2005.

For information and labs about how to secure your application, see my article " Securing a .NET Application on the Oracle Database". (Also, see the OTN .NET Developer Center for technical articles covering a range of Oracle.NET application lifecycle issues.)

Note that the free Oracle Developer Tools for Visual Studio, available for download from OTN, provides a Visual Studio add-in that makes the development of .NET apps on Oracle much easier and more intuitive. That subject is beyond our scope here, however.

.NET Data Provider

In addition to basic Oracle client connectivity software, .NET applications require the use of what is known as a managed data provider(where "managed" refers to code managed by the .NET framework). The data provider is the layer between the .NET application code and the Oracle client connectivity software. In almost every case, the best performance is achieved by using a provider optimized for a specific database platform instead of the generic .NET OLE DB data provider.

Oracle, Microsoft, and third-party vendors all offer .NET data providers optimized for Oracle. Oracle and Microsoft make their Oracle data providers available for free. (Microsoft's provider for the .NET Framework 2.0 is included in the framework, but it still requires Oracle client software installation.) In this article, we will use of the Oracle Data Provider for .NET (ODP.NET), which is included with the Oracle Database or as a separate download.

ODP.NET provides standard ADO.NET data access, while exposing Oracle database-specific features, such as XML DB, data access performance optimizations, and Real Application Clusters connection pooling.

When ODP.NET and Oracle client software are installed, application development using Visual Studio can begin. It's a good idea to confirm client connectivity before starting development. If you can connect to Oracle using Oracle client software such as SQL*Plus on the same machine as Visual Studio, then you know that your Oracle client-side software is properly installed and configured.

If you are new to Oracle, see the section "Installing .NET Products" in the  Oracle Database 2 Day Developer's Guide for background information regarding installing and configuring ODP.NET specifically, or to the  Oracle Database Documentation Library for general information about Oracle Database.

Creating a Project in Visual Studio 2005 or 2008

Let's create an ODP.NET application that retrieves data from an Oracle database. Later, we'll see how to perform error handling with ODP.NET and handle an additional data retrieval scenario.

After starting Visual Studio, the first task is to create a project. You can either select File | New | Project as shown below or click the New Project button located directly under File.

Figure 1 Creating a new project in Visual Studio 2008 Service Pack 1

New Project dialog box appears. On the left side of the dialog box under Project Types, select the programming language of your choice. In our example, "Visual Basic" was chosen. On the right side under Visual Studio installed templates, choose a project template. To keep things simple, a "Windows Forms Application" is selected.

Figure 2 Using the New Project dialog

You'll want to specify meaningful names for the project name (we used OraWinApp) and the solution name (we used OraWinApp). A solution contains one or more projects. When a solution contains only one project, many people use the same name for both.


Adding a Reference

Because our project must connect to an Oracle database, it is necessary to add a reference to the ODP.NET DLL containing the data provider of our choice. Within the Solution Explorer, select the project name, right click and select  Add Reference. Alternatively, you can go to the menu bar and select Project  and then select Add Reference.

Figure 3 Adding a reference

The Add Reference dialog box appears.

Figure 4 Selecting the ODP.NET Managed Data Provider

ODP.NET is found under the Oracle.DataAccess component name. Select Oracle.DataAccess from the list, then click OK to make the ODP.NET data provider known to your project.

Visual Basic/C# Statements

After adding references, it is standard practice to add Visual Basic Imports statements or C# using statements. Technically, these statements are not required but they do allow you to refer to database objects without using lengthy, fully qualified names.

By convention, these statements appear at or near the top of a code file, before the namespace or class declaration.

Imports Oracle.DataAccess.Client ' Visual Basic ODP.NET Oracle managed provider using Oracle.DataAccess.Client; // C# ODP.NET Oracle managed provider

If you added the reference, Intellisense will help you complete the addition of an Imports or using statement as shown in Figure 5.

Figure 5 Adding an Imports statement in Visual Basic

Connection Strings and Objects

An Oracle connection string is inseparable from Oracle names resolution. Suppose you had a database alias of OraDb defined in a tnsnames.ora file as follows:


OraDb=  
(DESCRIPTION=  
(ADDRESS_LIST=  
(ADDRESS=(PROTOCOL=TCP)(HOST=ORASRVR)(PORT=1521))  
)    
(CONNECT_DATA=     
(SERVER=DEDICATED)     
(SERVICE_NAME=ORCL)  
)   
) 

The OraDb alias defines the database address connection information for the client. To use the OraDb alias defined in the tnsnames.ora file shown above, you would use the following syntax:

Dim oradb As String = "Data Source=OraDb;User Id=scott;Password=tiger;" ' Visual Basic string oradb = "Data Source=OraDb;User Id=scott;Password=tiger;"; // C#

You can modify the connection string to obviate the need for the tnsnames.ora file, however. Simply replace the name of the alias with how it would be defined in a tnsnames.ora file.


' Visual Basic 
Dim oradb As String = "Data Source=(DESCRIPTION=" _       
+ "(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=ORASRVR)(PORT=1521)))" _   
+ "(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=ORCL)));" _   
+ "User Id=scott;Password=tiger;"  
// C# 
string oradb = "Data Source=(DESCRIPTION="       
+ "(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=ORASRVR)(PORT=1521)))"   
+ "(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=ORCL)));"   
+ "User Id=scott;Password=tiger;"; 

As you can see above, the username and password are embedded in the connection string in clear text. This is the simplest approach to creating a connection string. However, the clear text approach is undesirable from a security perspective. In particular, you must understand that compiled .NET application code is only marginally more secure than the clear text source code files. It is very easy to decompile .NET DLL and EXE files and view the original clear text contents. (Encryption is in fact the appropriate solution, but that subject would be a quite lengthy digression from our discussion here.)

Next, you must instantiate a connection object from the connection class. The connection string must be associated with the connection object.

Dim conn As New OracleConnection(oradb) ' Visual Basic OracleConnection conn = new OracleConnection(oradb); // C#

Notice that the connection string is associated with the connection object by being passed through the object's constructor, which is overloaded. The constructor's other overload allows the following alternative syntax:


Dim conn As New OracleConnection() ' Visual Basic 
conn.ConnectionString = oradb   
OracleConnection conn = new OracleConnection(); // C#
conn.ConnectionString = oradb;

After associating a connection string with a connection object, use the Open method to make the actual connection.


conn.Open() ' Visual Basic  
  conn.Open(); // C#

We'll cover error handling later.

Command Object

The Command object is used to specify the SQL command text that is executed, either a SQL string or a stored procedure. Similar to the Connection object, it must be instantiated from its class and it has an overloaded constructor. In this sample, ODP.NET will perform a SQL query to return the department name (DNAME) from the departments table (DEPT) where the department number (DEPTNO) is 10.


Dim sql As String = "select dname from dept where deptno = 10" ' Visual Basic
  Dim cmd As New OracleCommand(sql, conn)
  cmd.CommandType = CommandType.Text
  
  
  string sql = "select dname from dept where deptno = 10"; // C#
  OracleCommand cmd = new OracleCommand(sql, conn);
  cmd.CommandType = CommandType.Text;

Using different overloads, the syntax can be structured slightly differently. The Command object has methods for executing the command text, which will be seen in the next section. Different methods are appropriate for different types of SQL commands.

Retrieving a Scalar Value

Retrieving data from the database can be accomplished by instantiating an OracleDataReader object and using the ExecuteReader method, which returns an OracleDataReader object. Returned data is accessible by passing either the column name or zero-based column ordinal to the OracleDataReader.


Dim dr As OracleDataReader = cmd.ExecuteReader() ' Visual Basic
  dr.Read()
  
  
Label1.Text = dr.Item("dname") ' retrieve by column name
  Label1.Text = dr.Item(0) ' retrieve the first column in the select list
  Label1.Text = dr.GetString(0) ' return a .NET data type
  Label1.Text = dr.GetOracleString(0) ' return an Oracle data type

There are typed accessors for returning .NET native data types and others for returning native Oracle data types, all of which are available in C#, Visual Basic, or any other .NET language. Zero-based ordinals are passed to the accessors to specify which column to return.



OracleDataReader dr = cmd.ExecuteReader(); // C#
  dr.Read();  
  label1.Text = dr["dname"].ToString(); // C# retrieve by column name 
  label1.Text = dr.GetString(0).ToString();  // return a .NET data type 
  label1.Text = dr.GetOracleString(0).ToString();  // return an Oracle data type 

In this simplified example, the returned value of DNAME is a string and is used to set the value of the label control's text property, which is also a string. But if DEPTNO, which is not a string, had been retrieved instead, there would be a data type mismatch. The .NET runtime attempts to implicitly convert from one data type to another when the source and destination data types don't match. Sometimes the data types are incompatible and the implicit conversion fails, throwing an exception. But even when it works, it's still better to use explicit data type conversions instead of implicit data type conversion.

An explicit cast to integer is shown below: Label1.Text = CStr(dr.Item("deptno")) ' Visual Basic integer to string cast

C# is not as forgiving as Visual Basic on implicit conversions. You'll find yourself doing explicit conversions:

label1.Text = dr.GetInt16("deptno").ToString(); // C#

You can explicitly cast scalar values as well as arrays.

Close and Dispose

Either the connection object's Close or the Dispose method should be called to close the connection to the database. The Dispose method calls the Close method.



conn.Close()   ' Visual Basic
  conn.Dispose() ' Visual Basic
  
  
 conn.Close();   // C#
  conn.Dispose(); // C# 
  

You don't have to explicitly call Close  or  Dispose if you use VB's  Using  keyword or C#'s using  keyword.



using (OracleConnection conn = new OracleConnection(oradb)) // C#  
{     
conn.Open();  
OracleCommand cmd = new OracleCommand();   
cmd.Connection = conn;    
cmd.CommandText = "select dname from dept where deptno = 10";  
cmd.CommandType = CommandType.Text;     
OracleDataReader dr = cmd.ExecuteReader();  
dr.Read();     
label1.Text = dr.GetString(0); 
}

In addition, OracleCommand includes a Dispose method; OracleDataReader includes a Close and Dispose method. Closing and disposing .NET objects free up system resources, ensuring more efficient application performance, which is especially important under high load conditions. You can experiment with some of the concepts we've learned here in  Lab 1 (Retrieving Data from the Database) and Lab 2 (Adding Interactivity).

Error Handling

When an error occurs, .NET applications should gracefully handle the error and inform the user with a meaningful message. Try-Catch-Finally structured error handling is a part of .NET languages; here is a relatively minimalist example of using the Try-Catch-Finally syntax:


' Visual Basic>
  Try
  conn.Open()
   Dim cmd As New OracleCommand
  cmd.Connection = conn
  cmd.CommandText = "select dname from dept where deptno = " + TextBox1.Text
  cmd.CommandType = CommandType.Text
    If dr.Read() Then
  Label1.Text = dr.Item("dname") ' or use dr.Item(0)
  End If
  Catch ex As Exception ' catches any error
  MessageBox.Show(ex.Message.ToString())
  Finally
  ' In a real application, put cleanup code here.
  End Try
// C#
  try
  {
  conn.Open();
   OracleCommand cmd = new OracleCommand();
  cmd.Connection = conn;
  cmd.CommandText = "select dname from dept where deptno = " + textBox1.Text;
  cmd.CommandType = CommandType.Text;
   if (dr.Read()) // C#
  {
  label1.Text = dr["dname"].ToString();
  // or use dr.GetOracleString(0).ToString()
  }
  }
  catch (Exception ex) // catches any error
  {
  MessageBox.Show(ex.Message.ToString());
  }
  finally
  {
  // In a real application, put cleanup code here.
  }

Although this approach will gracefully capture any errors in attempting to get data from the database, it is not user friendly. For example, look at the following message displayed when the database is unavailable:

Figure 6 An ORA-12545 error caught and displayed to the user

An ORA-12545 is quite meaningful for an Oracle DBA or developer, but not for an end user. A better solution is to add an additional Catchstatement to trap for the most common database errors and provide user-friendly messages.


Catch ex As OracleException ' catches only Oracle errors  
    Select Case ex.Number 
	Case 1      
	MessageBox.Show("Error attempting to insert duplicate data.") 
	Case 12545         
	MessageBox.Show("The database is unavailable.")   
	Case Else       
	MessageBox.Show("Database error: " + ex.Message.ToString())   
	End Select  Catch ex As Exception ' catches any error  
    MessageBox.Show(ex.Message.ToString()) 
	catch (OracleException ex) // catches only Oracle errors
	{    
	switch (ex.Number)    
	{        
	case 1:       
	MessageBox.Show("Error attempting to insert duplicate data.");  
	break;        
	case 12545:    
	MessageBox.Show("The database is unavailable.");     
	break;       
	default:      
	MessageBox.Show("Database error: " + ex.Message.ToString());   
	break;    
	} 
	} 
	catch (Exception ex) // catches any error not previously caught
	{   
	MessageBox.Show(ex.Message.ToString()); 
	} 

Notice the two Catch statements in the code sample above. If there aren't any Oracle errors to catch, the first statement branch is skipped, leaving any other non-Oracle error to be caught by the second statement. Catch statements must be ordered in the code from most specific to most general. After implementing the user-friendly exception handling code, the ORA-12545 error message appears as follows:

Figure 7 A user-friendly error message for an ORA-12545 error

The Finally   code block is always executed regardless of whether or not an error occurred. It is where cleanup code belongs. If you don't useUsing   or using , you should dispose your connection and other objects in the Finally   code block.

Retrieving Multiple Values Using a DataReader

So far our examples have only showed how to retrieve a single value. An OracleDataReader can retrieve values for multiple columns and multiple rows. First consider a multiple column, single row query:

select deptno, dname, loc from dept where deptno = 10

To obtain the values of the columns, either zero-based ordinals or column names can be used. Ordinals are relative to the order in the query. Thus, the LOC column's value can be retrieved in Visual Basic by using either dr.Item(2) or dr.Item("loc").

Here is a code snippet that concatenates the DNAME and LOC columns from the previous query:


Label1.Text = "The " + dr.Item("dname") + " department is in " + dr.Item("loc") ' VB

label1.Text = "The " + dr["dname"].ToString() + " department is in " + 

dr["loc"].ToString();  // C#

Now consider a query that returns multiple rows:

select deptno, dname, loc from dept  

To process multiple rows returned from an OracleDataReader, some type of looping construct is needed. Furthermore, a control that can display multiple rows is desirable. An OracleDataReader is a forward-only, read-only cursor, so it can't be bound to an updateable or fully scrollable control such as a Windows Forms DataGrid control. An OracleDataReader is compatible with a ListBox control, as the following code snippet illustrates:


While dr.Read() ' Visual Basic   
  ListBox1.Items.Add("The " + dr.Item("dname") + " department is in " + dr.Item("loc"))
  End While  
  while (dr.Read()) // C# 
  {    
  listBox1.Items.Add("The " + dr["dname"].ToString() + " department is in " +     
  dr["loc"].ToString()); 
  } 


Lab 3
 (Retrieve Multiple Columns and Rows with an OracleDataReader) highlights some of these concepts.

Building and Running on x64

When running Visual Studio 2008 on an x64 operating system, the Active solution platform defaults to Any CPU. Change that to x86 before building your project.

Figure 8 Change from Any CPU to x86 when building on a 64-bit platform

Conclusion

This article has introduced you to the process of accessing Oracle databases using .NET programming languages. You should now have the capability to connect to the database and retrieve multiple columns and rows.

Lab 1: Retrieving Data from the Database

We begin with the requirement that you've created a project and added a reference as shown previously in this article.

1. Continue by adding a button control and a label control to the Windows form. Be sure to leave room above the controls to allow additions that will be made in Lab 2.

Figure 9 Lab 1 form with button and label controls

2. Add code to retrieve data from the Oracle database and display the results on the form. Put the code in a click event handler for the button. The easiest way to get started with this task is to double click the button because it will create a stub for the event handler.

Figure 10 Click event handler stub

3. Add Visual Basic Imports statements before the Public Class declaration or C# using statements before the namespace declaration.



Imports Oracle.DataAccess.Client ' Visual Basic, ODP.NET Oracle managed provider  
			using Oracle.DataAccess.Client; // C#, ODP.NET Oracle managed provider 

4. Add the Visual Basic version of the click event handler code between the Private Sub and End Sub statements (be sure to replace ORASRVR with your server's host name):



Dim oradb As String = "Data Source=(DESCRIPTION=(ADDRESS_LIST=" _ 
 
 + "(ADDRESS=(PROTOCOL=TCP)(HOST=ORASRVR)(PORT=1521)))" _      
 + "(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=ORCL)));" _        
 + "User Id=scott;Password=tiger;" 
 Dim conn As New OracleConnection(oradb) ' Visual Basic 
 conn.Open()  
 Dim cmd As New OracleCommand 
 cmd.Connection = conn 
 cmd.CommandText = "select dname from dept where deptno = 10" 
 cmd.CommandType = CommandType.Text  
 Dim dr As OracleDataReader = cmd.ExecuteReader() 
 dr.Read()  ' replace this statement in next lab 
 Label1.Text = dr.Item("dname") ' or dr.Item(0), remove in next lab  
 dr.Dispose() 
 cmd.Dispose()
 conn.Dispose() 

Add the following C# code to the click event handler between the { and } curly braces for the button's click event handler (be sure to replace ORASRVR with your server's host name):



 string oradb = "Data Source=(DESCRIPTION=(ADDRESS_LIST="   
 + "(ADDRESS=(PROTOCOL=TCP)(HOST=ORASRVR)(PORT=1521)))"    
 + "(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=ORCL)));"   
 + "User Id=scott;Password=tiger;";  
 OracleConnection conn = new OracleConnection(oradb); // C# 
 conn.Open();  
 OracleCommand cmd = new OracleCommand();
 cmd.Connection = conn; 
 cmd.CommandText = "select dname from dept where deptno = 10"; 
 cmd.CommandType = CommandType.Text; 
 OracleDataReader dr = cmd.ExecuteReader();  dr.Read(); 
 // replace this statement in next lab  label1.Text = dr["dname"].ToString();  
 // remove in next lab    dr.Dispose();  cmd.Dispose();  conn.Dispose();  

5. Run the application. Click the button. You should see the following:

Figure 11 Data successfully retrieved.

Lab 2: Adding Interactivity

Now that the basics of database access are implemented in the code, the next step is to add interactivity to the application. Instead of running the hard coded query, a textbox control can be added to accept a user input for the department number (i.e., DEPTNO).

1. Add a textbox control and another label control to the form as shown below. Set the text property of the Label2  control to  Enter Deptno:  and make sure that the  Text property of  TextBox1  isn't set to anything.

Figure 12 Lab 2 form with button and label controls

2. Modify the code that defines the select string:

cmd.CommandText = "select dname from dept where deptno = " + TextBox1.Text 'VB cmd.CommandText = "select dname from dept where deptno = " + textBox1.Text; // C#>

3.

4. Run the application. Test the application by entering 10 for the DEPTNO. Retest the application by entering an invalid DEPTNO (e.g., 50). The application will abort.

5

Figure 13 An unhandled exception

6

7. Modify your code to prevent an error when an invalid DEPTNO is entered. Recall that the ExecuteReader method actually returns an object. Replace the line containing dr.Read with all of the following statements.


  If dr.Read() Then ' Visual Basic    
  Label1.Text = dr.Item("dname").ToString() 
  Else    
  Label1.Text = "deptno not found"
  End If  
  if (dr.Read()) // C# 
  {    
  label1.Text = dr["dname"].ToString();; 
  } 
  else
  {    
  label1.Text = "deptno not found";
  }  

Test the application by entering a DEPTNO that does not exist. Now the application no longer aborts. Enter the letter A instead of a number and click the button. The application aborts. Clearly, our application needs a better approach to handling errors.Although it could be argued that the application should not allow the user to make invalid inputs that would cause an error, ultimately the application must have robust error handling added. Not all errors are preventable, so error handling must be implemented.

Lab 3: Retrieve Multiple Columns and Rows with an OracleDataReader

Now that a single value has been retrieved, the next step is to retrieve multiple columns and rows with an OracleDataReader. A ListBox control is added to the form to display the results.

1. Add a ListBox control to the form. Resize the control to fill most of the width of the form as shown below.

Figure 14 Form with ListBox added

Remove the where clause from the query and add the additional columns:



  cmd.CommandText = "select deptno, dname, loc from dept" ' Visual Basic 
  cmd.CommandText = "select deptno, dname, loc from dept"; // C# 

3

4. The query results will be read in a while loop and will populate the ListBox control. Modify your Visual Basic code to look like this:


 Dim oradb As String = "Data Source=(DESCRIPTION=(ADDRESS_LIST=" _   
 + "(ADDRESS=(PROTOCOL=TCP)(HOST=ORASRVR)(PORT=1521)))" _       
 + "(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=ORCL)));" _         
 + "User Id=scott;Password=tiger;"  
 Dim conn As New OracleConnection(oradb) ' Visual Basic  conn.Open()  
 Dim cmd As New OracleCommand 
 cmd.Connection = conn 
 cmd.CommandText = "select deptno, dname, loc from dept" 
 cmd.CommandType = CommandType.Text 
 Dim dr As OracleDataReader = cmd.ExecuteReader() 
 While dr.Read()   
 ListBox1.Items.Add("The " + dr.Item("dname") + _     
 " department is in " + dr.Item("loc")) 
 End While  
 dr.Dispose() 
 cmd.Dispose()
 conn.Dispose() 
 Modify your C# code to look like this: 
 string oradb = "Data Source=(DESCRIPTION=(ADDRESS_LIST="     
 + "(ADDRESS=(PROTOCOL=TCP)(HOST=ORASRVR)(PORT=1521)))"    
 + "(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=ORCL)));"         
 + "User Id=scott;Password=tiger;";  
 OracleConnection conn = new OracleConnection(oradb); // C# 
 conn.Open(); 
 OracleCommand cmd = new OracleCommand();
 cmd.Connection = conn; 
 cmd.CommandText = "select deptno, dname, loc from dept"; 
 cmd.CommandType = CommandType.Text;  
 OracleDataReader dr = cmd.ExecuteReader();
 while (dr.Read())
 {    
 listBox1.Items.Add("The " + dr["dname"].ToString() +   
 " department is in " + dr["loc"].ToString()); 
 }   
 dr.Dispose(); 
 cmd.Dispose(); 
 conn.Dispose(); 

5.

6. Run the application. The ListBox should be populated with all of the department names and locations from the DEPT table. The code downloads have error handling implemented.

John Paul Cook [ johnpaulcook@email.com] is a database and .NET consultant based in Houston. He is the author of numerous articles on .NET, Oracle, and virtualization and has been developing relational database applications since 1986. His current interests include Visual Studio 2008 and Oracle Database 11g. He is an Oracle certified DBA and a Microsoft Most Valuable Professional.