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McGregorWang

Get Started with the Enterprise Library Data Access Application Block

Introduction
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The Enterprise Library Data Access Application Block is the new version of the Microsoft Data Access Application Block (DAAB). Whereas the previous DAAB was a stand-alone application block, the new DAAB is a part of the new Enterprise Library collection of application blocks. You can obtain the most recent version of the library from the Patterns & Practices Enterprise Library Developer Center.

Last week, I spent one whole day trying to figure out how to configure and work with the new Data Access Application Block. This was due to few resources being available on the web. I even visited the Data Access Application Block forum at the ASP.NET Forums, but found few good resources to start with. Even with the few articles I found, I was not immediately successful in learning how to use the different methods available in the new Enterprise Library.

For the above reasons, I decided to write this article; not to explain how to configure the Enterprise Library, but rather to provide sample codes that can be used in a data-driven ASP.NET website.

Outline

In this article, I will start by listing the methods in the Enterprise Library Data Access Application Block (which, from now on, I will refer to as EN-DAAB) that can be used to interact with the database. Then, I will show you how to define the EN-DAAB configuration section in either the App.config or Web.config configuration file. Later, I will present sample code for each method, to show how easy it is to work with those methods. Finally, I will recommend some online websites that you can visit and check the latest news on the EN-DAAB.

Enterprise Library Data Access Methods

The EN-DAAB contains a set of useful methods that can save developers from having to write their own methods for common database functions.

As you may know, the EN-DAAB allows you to interact with different databases including Microsoft SQL Server, Oracle, and IBM DB2. However, when using its methods, you will not notice the difference whether using SQL Server, Oracle, or any other database provider. Everything is encapsulated within those methods, forming a strong abstraction layer that hides from the developer the details of interacting with a particular database. Let us have a look at each method and give a brief explanation of its function.

  1. CreateDatabase(): This method is used to create a new instance of the database being used in the application, called a database object.
  2. ExecuteReader("ReaderName"): This method returns an IDataReader object.
  3. ExecuteDataSet("DataSetName"): This method returns a DataSet object.
  4. LoadDataSet(“DataSetName”): This method fills an existing DataSet object.
  5. ExecuteNonQuery(dbCommandWrapper): This method is used to execute a query that returns a set of fields in a row, and to insert, delete, and update records.
  6. ExecuteScalar(dbCommandWrapper): This method is used only when you want to retrieve a single value from the database.

Define the Configuration

The EN-DAAB requires a configuration file in order to function properly. If you are developing a Windows Forms application, the configuration file is named App.config. On the other hand, if you are developing an ASP.NET web application, the configuration file is named Web.config.

Now the question is how to configure the EN-DAAB? The answer is simple: follow the steps below.

Step1: From the Windows Start menu, navigate to Programs, Microsoft patterns & practices, Enterprise Library, Enterprise Library Configuration. Once you open the Enterprise Library Configuration program, you will see the following window:

Step2: Right-click on the Enterprise Library Configuration node and choose New Application.

Step3: Right-click on the new Application1 node, and select New, Data Access Application block.

You can see in the above figure the Configuration Application Block and the Data Access Application Block. I will first configure the Configuration Block, and then move to the other block.

Step4: Click on the dataConfiguration node and look at the right window. You have the choice of whether to encrypt the configuration section. I will choose not to encrypt the configuration file by setting the value of Encrypt to False.

Step5: Click on the XML File Storage Provider node to specify the filename that will hold the configuration in your application and the XML File Storage Provider. Rename the second field to XmlProvider and leave the first field as it is. Now, click on the Xml Serializer Transformer node, and rename this field to XmlTransformer.

Step6: In this step, I will configure the Data Access Application Block node. This node contains three child nodes:

  1.   Connection Strings
  2. Database Instances
  3.   Database Types

The Connection Strings node is the place where you add the connection string to your database. In this article I will choose to connect to a SQL database. Once you expand the Connection Strings node you will see a default connection string. Click on the Sql Connection String node, and in the right window you have the option of renaming the connection string. To configure the connection string, expand the Sql Connection String node, and you will see that there are three parameters:

  1. Database
  2. Integrated Security
  3. Server

Click on Database parameter, and in the right window write Northwind in the Value field. Then, click on the Server parameter, and in the right window put localhost in the Value field.  Leave all other parameters as they are, although you could have given them names according to your preferences. Note that you can add additional parameters to the connection string by right clicking on Sql Connection String node and adding other parameters.

The other two nodes, Database Instances and Database Types, can be left with their default values.

After you finish all the steps, open File menu item and select Save Application. When you are prompted to choose a file name, choose either the Web.config or the App.config file in your application.

Now that you have seen how to configure the EN-DAAB, let us put the application block into action.

Code Samples

In this section we are going to present a code sample for each of the methods listed above. With these samples you should get a better understanding of how to use these methods while developing your data access methods.

Be sure to add references to the following assemblies:

   Microsoft.Practices.EnterpriseLibrary.Configuration.dll
   Microsoft.Practices.EnterpriseLibrary.Data.dll

You can find these assemblies in the following path:

   [Drive Name]:/Program Files/Microsoft Enterprise Library/bin

In each code file you will need to include the following lines:

   using Microsoft.Practices.EnterpriseLibrary.Configuration;
   using Microsoft.Practices.EnterpriseLibrary.Data;

The database used for the following code samples is the Northwind database that ships with Microsoft SQL Server, and the data table used is the Customers table.

 
Generate a DataReader Object
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This code sample shows how to get a DataReader object using the ExecuteDataReader() method.

Below is the stored procedure that returns all records from the Customers table.

Listing 1 

CREATE PROCEDURE [dbo].[GetCustomerList]
AS
SET NOCOUNT ON
   SELECT
      *
   FROM 
      [Customers]
GO

The following C# code executes the above stored procedure and obtains the result as a DataReader object:

Listing 2

try
{
   // Create DataBase Instance
   Database db = DatabaseFactory.CreateDatabase();
   // Initialize the Stored Procedure
   DBCommandWrapper dbCommandWrapper = GetStoredProcCommandWrapper("GetCustomerList");
   using (IDataReader dataReader = db.ExecuteReader(dbCommandWrapper))
   { 
      while (dataReader.Read())
      {  
         Response.Write("CustomerID : " +
            dataReader["CustomerID"].ToString()+"
");
         Response.Write("CompanyName : " +
         dataReader["CompanyName"].ToString()+"

");
      }
   }
}
catch (Exception ex)
{
   Response.Write(ex.ToString());
}

As you can see, I start by instantiating a new database object as follows:

    Database db = DatabaseFactory.CreateDatabase();

Then, I define a wrapper object which encapsulates the stored procedure’s name.

   DBCommandWrapper dbCommandWrapper = GetStoredProcCommandWrapper("GetCustomerList");

Finally, using the generated DataReader object, I was able to display the CustomerID and CompanyName values for each record in the Customers table.

using (IDataReader dataReader = db.ExecuteReader(dbCommandWrapper))
   { 
      while (dataReader.Read())
      {
Generate a DataSet Object
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This code sample shows how to get a DataSet object using the ExecuteDataSet() method. The same stored procedure used above in Listing 1 is used in this sample code.

Listing 3

try
{
   // Create DataBase Instance
   Database db = DatabaseFactory.CreateDatabase();
   // Initialize the Stored Procedure
   DBCommandWrapper dbCommandWrapper =
   db.GetStoredProcCommandWrapper("GetCustomerList");
   // Generate DataSet object
   DataSet ds = null;
   ds = db.ExecuteDataSet(dbCommandWrapper);
   // Fill DataGrid
   if ( ds.Tables[0].Rows.Count > 0 )
   {   
      // Supposing we have a datagrid whose id is DataGrid1
      DataGrid1.DataSource = ds.Tables[0].DefaultView;
      DataGrid1.DataBind();
   }
   else
      Response.Write("No rows were selected");
}
catch (Exception ex)
{
   Response.Write(ex.ToString());
}

The same initial steps are used in this code sample as in the previous code sample. However, in this sample I am generating a DataSet object, and then using the following code to check whether the DataSet contains any records:

   if ( ds.Tables[0].Rows.Count > 0 )

Based on that check, I choose whether to bind the DefaultView of the DataSet to a DataGrid, or to show a message indicating that no records were returned.
Retrieve a Single Row
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To retrieve a single row from a database data table, it is recommended that you use a DataReader object. First of all, a SQL Server stored procedure is shown, then followed by the C# code that will execute the stored procedure and return a DataReader object, holding a single row.

Below is the stored procedure that returns a single record from the Customers table.

Listing 4

CREATE PROCEDURE [dbo].[GetOneCustomer]
(
   @CustomerID NCHAR(5)
)
AS
SET NOCOUNT ON
   SELECT
      *
   FROM
      [Customers]
   WHERE
      [CustomerID] LIKE @CustomerID
GO

The following C# code executes the above stored procedure and obtains a single row in a DataReader object:

Listing 5

try
{
   // Create DataBase Instance
   Database db = DatabaseFactory.CreateDatabase();
   // Initialize the Stored Procedure
   DBCommandWrapper dbCommandWrapper = db.GetStoredProcCommandWrapper("GetOneCustomer");
   dbCommandWrapper.AddInParameter("@CustomerID",DbType.String,"ALFKI");
   using (IDataReader dataReader = db.ExecuteReader(dbCommandWrapper))
   { 
      if (dataReader.Read())
      {
         Response.Write("CustomerID : " + dataReader["CustomerID"].ToString()+"
");
         Response.Write("CompanyName : " + dataReader["CompanyName"].ToString()+"

");
      }
   }
}
catch (Exception ex)
{
   Response.Write(ex.ToString());
}

As you can see in the code above, a new method of the dbCommandWrapper class was used, which is the AddInParameter() method. In the above sample code, this method is used to pass the required @CustomerID parameter to the stored procedure.

The stored procedure in this code sample will query the Customers table and retrieve the row where the CustomerID column matches the CustomerID parameter provided. This explains the need to add an input parameter to the dbCommandWrapper object, as it is a parameter that is required by the stored procedure. In addition to the AddInputParameter() method, there is the AddOutputParameter() method, which I will address in the next section.
Retrieve More than One Column in a Row
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The code sample above retrieves an entire record from a database table. Sometimes however we need only specific fields from a row in a database table. In this case we need to supply the stored procedure with not only an input parameter as in the previous section, but also one or more output parameters to store the result of the stored procedure.

The following is an example of a stored procedure which will take as input the CustomerID value and return only two fields: CompanyName and ContactName. For this limited result set, we have to use the AddOutputParameter() method. This method is used to return the output of a stored procedure.

It is recommended when executing a stored procedure with output parameters to use the ExecuteNonQuery() method instead of the ExecuteDataReader() method.

The SQL stored procedure is as follows:

Listing 6

CREATE PROCEDURE [dbo].[GetCustomerMultipleFields]
(
   @CustomerID NCHAR(5),
   @CompanyName NVARCHAR(40) OUTPUT,
   @ContactName NVARCHAR(30) OUTPUT
) 
AS
SET NOCOUNT ON
   SELECT
      @CompanyName = [CompanyName],
      @ContactName = [ContactName]
   FROM
      [Customers]
   WHERE
      [CustomerID] LIKE @CustomerID
GO

The following C# code executes the above stored procedure and uses the AddOutputParameter() method to obtain the results:

Listing 7

try
{
   // Create DataBase Instance
   Database db = DatabaseFactory.CreateDatabase();
   // Initialize the Stored Procedure
   DBCommandWrapper dbCommandWrapper = db.GetStoredProcCommandWrapper("GetCustomerMultipleFields");
   dbCommandWrapper.AddInParameter("@CustomerID", DbType.String, "ALFKI");
   dbCommandWrapper.AddOutParameter("@CompanyName", DbType.String, 40);
   dbCommandWrapper.AddOutParameter("@ContactName", DbType.String, 30);
   //Execute the stored procedure
   db.ExecuteNonQuery(dbCommandWrapper);
   //Display results of the query
   string results = string.Format("Company Name : {0}, Contact Name {1},",
        dbCommandWrapper.GetParameterValue("@CompanyName"),
        dbCommandWrapper.GetParameterValue("@ContactName"));
   Response.Write(results);
}
catch (Exception ex)
{
   Response.Write(ex.ToString());
}

In the above code, I passed a customer ID value to the stored procedure as an input parameter. As the stored procedure is designed to return two values, CompanyName and ContactName, these were identified as output parameters.

To display the returned values we used another method of dbCommandWrapper, which is GetParameterValue(“ParameterName”). This method returns the value of the parameter specified.
Retrieve a Single Field
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This is the case where one needs to retrieve a single column of a row inside a database data table. However, if you are just selecting a single column in a row based on a certain primary key, then no need to use output parameters, instead use the ExecuteScalar() method, which will return the single selected column in the stored procedure. The stored procedure used in this section is as follows:

Listing 8

CREATE PROCEDURE [dbo].[GetCustomerSingleColumn]
(
   @CustomerID NCHAR(5)
)
AS
SET NOCOUNT ON
   SELECT 
      [CompanyName] 
   FROM 
      [Customers]
   WHERE 
      [CustomerID] LIKE @CustomerID
GO

The C# code used to execute the above stored procedure is as follows:

Listing 9

try
{
   // Create DataBase Instance
   Database db = DatabaseFactory.CreateDatabase();
   // Initialize the Stored Procedure
   DBCommandWrapper dbCommandWrapper = db.GetStoredProcCommandWrapper("GetCustomerSingleColumn");
   dbCommandWrapper.AddInParameter("@CustomerID", DbType.String, "ALFKI");
   //Execute the stored procedure
   string GetCompanyName = (string) db.ExecuteScalar(dbCommandWrapper);
   //Display results of the query
   string results = string.Format("Company Name : {0}",GetCompanyName);
   Response.Write(results);
}
catch (Exception ex)
{
   Response.Write(ex.ToString());
}

The code is straight forward. I am using ExecuteScalar method to retrieve the returned value, in this case the CompanyName, and then writing the company name to the page.
Insert a New Record
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This code sample shows how to insert a new record into the Customers table.

The stored procedure that is used is as follows:

Listing 10

CREATE PROCEDURE InsertRecordIntoCustomer
(
   @CustomerID NCHAR(5),
   @CompanyName VARCHAR(50)
)
AS
DECLARE @Result int
IF EXISTS
(
   SELECT
      NULL
         FROM
      [Customers]
         WHERE
      [CustomerID] LIKE @CustomerID
) 
   BEGIN
      SELECT @Result = -1
      END
ELSE
   BEGIN
      INSERT INTO [Customers]
         (
         [CustomerID],
         [CompanyName]
         )
         VALUES
         (
         @CustomerID,
         @CompanyName
         )
      SELECT @Result = @@ERROR
      END
RETURN @Result
GO

The procedure starts by checking whether the record to insert is already present in the Customers table. If it is found, a value of -1 is returned. If not, the record is inserted and a value of 0 is returned.

The following C# code will execute the above stored procedure. Executing the above stored procedure includes both input and output parameters. Therefore, it is recommended that the ExecuteNonQuery() method is used.

Listing 11

try
{
   // Create DataBase Instance
   Database db = DatabaseFactory.CreateDatabase();
   // Initialize the Stored Procedure
   DBCommandWrapper dbCommandWrapper = db.GetStoredProcCommandWrapper("InsertRecordIntoCustomer");
   // If There are output parameters, use ExecuteNonQuery only, better performance
   dbCommandWrapper.AddInParameter("@CustomerID", DbType.String, "JohnY");
   dbCommandWrapper.AddInParameter("@CompanyName", DbType.String, "Microsoft");
   object Internalvalue = new object();
   dbCommandWrapper.AddParameter("@Result", DbType.Int32, ParameterDirection.ReturnValue,
        "@Result", DataRowVersion.Default,Internalvalue);
   // Get output
   int GetResult = 0;
   // Execute Stored Procedure
   db.ExecuteNonQuery(dbCommandWrapper);
   GetResult = (int)dbCommandWrapper.GetParameterValue("@Result");
   switch ( GetResult )
   {
      case 0:
         Response.Write("Record Inserted.");
         break;
      case -1: 
         Response.Write("Record Already Found.");
         break;
      default:
         Response.Write("Record Not Inserted.");
         break;
   }
}
catch (Exception ex)
{
   Response.Write(ex.ToString());
}

As you can see, the code is very simple. Two input parameters are added to the dbCommandWrapper, representing part of the record to be inserted in the Customers table. A return parameter is also added, representing the result returned by the stored procedure that indicates whether the record was inserted successfully or not. Once again, notice the use of ExecuteNonQuery() method to perform this task.
Update a Record
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This code sample shows how to update an existing record in the Customers table.

The stored procedure that is used is as follows:

Listing 12

CREATE PROCEDURE [dbo].[CustomersUpdate]
(
   @CustomerID NCHAR(5),
   @CompanyName NVARCHAR(40)
)
AS
SET NOCOUNT ON
DECLARE @Result INT
IF NOT EXISTS
(
    SELECT   
      NULL
         FROM   
      [Customers]
         WHERE
      [CustomerID] LIKE @CustomerID
) 
   BEGIN
      SELECT @Result = -1
         END
ELSE
   BEGIN
      UPDATE   
         [Customers]  
      SET  
         [CompanyName] = @CompanyName  
      WHERE  
         [CustomerID] = @CustomerID  
      
      SELECT @Result = @@ERROR
   END
RETURN @Result
GO
CREATE PROCEDURE [dbo].[GetCustomerList]
AS
SET NOCOUNT ON
   SELECT
      *
   FROM 
      [Customers]
GO

This stored procedure operates in a manner similar to that shown in the previous code sample. The procedure starts by checking whether the record to be updated already exists. If the record does not exist in the data table a value of -1 is returned. If it exists, the record is updated and a value of 0 is returned.

The following C# code updates a data table record:

Listing 13

try
{
   // Create DataBase Instance
   Database db = DatabaseFactory.CreateDatabase();
   // Initialize the Stored Procedure
   DBCommandWrapper dbCommandWrapper = db.GetStoredProcCommandWrapper("CustomersUpdate");
   // If There are output parameters, use ExecuteNonQuery only, better performance
   dbCommandWrapper.AddInParameter("@CustomerID", DbType.String, "Wessam");
   dbCommandWrapper.AddInParameter("@CompanyName", DbType.String, "TerraVision");
   object Internalvalue = new object();
   dbCommandWrapper.AddParameter("@Result", DbType.Int32, ParameterDirection.ReturnValue, 
        "@Result", DataRowVersion.Default, Internalvalue);
   // Get output
   int GetResult = 0;
   // Execute Stored Procedure
   db.ExecuteNonQuery(dbCommandWrapper);
   GetResult = (int)dbCommandWrapper.GetParameterValue("@Result");
   switch ( GetResult )
   {
      case 0:
         Response.Write("Record Updated.");
         break;
      case -1: 
         Response.Write("Record Not Found.");
         break;
      default:
         Response.Write("Record Not Updated.");
         break;
   }
}
catch (Exception ex)
{
   Response.Write(ex.ToString());
}

The above code is straight forward. Input and output parameters were added to the dbCommandWrapper object. An output parameter is added that represents the result returned by the stored procedure about the status of the update process.  Then a call to execute the stored procedure was issued. If the returned value is zero, this means that the record was inserted successfully and the message “Record Updated” is written to the page. On the other hand, if the returned value is -1, this means that the record to be updated was not found in the data table, and the message “Record Not Found” is written to the page. Any other value of the returned variable means that an unknown error has occurred and the following message is written to the page: “Record Not Updated”.
Delete a Record
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The previous code samples showed how to retrieve, insert, and update data in a database. This final code sample shows how to delete a record from a database table.

Following is the stored procedure used to delete a record from the Customers table.

Listing 14

CREATE PROCEDURE [dbo].[CustomersDelete]
(
   @CustomerID NCHAR(5)
)
AS
SET NOCOUNT ON
DECLARE @Result INT
IF NOT EXISTS
(
    SELECT
      NULL
         FROM   
      [Customers]
         WHERE
      [CustomerID] LIKE @CustomerID
)
   BEGIN
      SELECT @Result = -1
         END
ELSE
   BEGIN
      DELETE 
         [Customers]
      WHERE 
         [CustomerID] LIKE @CustomerID
                 
      SELECT @Result = @@ERROR
         END
RETURN @Result
GO

Once again the stored procedure starts by checking whether the record to be deleted actually exists in the database table. If not found, a value of -1 is returned, otherwise the record is deleted and a value of 0 is returned.

The following C# code shows how to run the above stored procedure:

Listing 15

try
{
   // Create DataBase Instance
   Database db = DatabaseFactory.CreateDatabase();
   // Initialize the Stored Procedure
   DBCommandWrapper dbCommandWrapper = db.GetStoredProcCommandWrapper("CustomersDelete");
   // If There are output parameters, use ExecuteNonQuery only, better performance
   dbCommandWrapper.AddInParameter("@CustomerID", DbType.String, "JohnY");
   object Internalvalue = new object();
   dbCommandWrapper.AddParameter("@Result", DbType.Int32, ParameterDirection.ReturnValue, 
        "@Result", DataRowVersion.Default, Internalvalue);
   // Get output
   int GetResult = 0;
   // Execute Stored Procedure
   db.ExecuteNonQuery(dbCommandWrapper);
   GetResult = (int)dbCommandWrapper.GetParameterValue("@Result");
   switch ( GetResult )
   {
      case 0:
         Response.Write("Record Deleted.");
         break;
      case -1: 
         Response.Write("Record Not Found.");
         break;
      default:
         Response.Write("Record Not Deleted.");
         break;
   }
}
catch (Exception ex)
{
   Response.Write(ex.ToString());
}

In the above code, an input parameter is added to the dbCommandWrapper class to be able to execute the stored procedure. A return parameter is also added that represents the result returned by the stored procedure about the status of the delete process. As in the previous code sample, the returned value is checked against three different values. If it has a value of zero, this means the record was deleted successfully, and a message “Record Deleted” is written to the page. If it has a value of -1, this means that the record to be deleted was not found in the database, and a message “Record Not Found” is written to the page. Finally, any other value means that an error occurred when the stored procedure was executing, and a message “Record Not Deleted” is written to the page.
Online Resources
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In this section, I will recommend some useful online resources that you should visit often in order to keep track of updates to the EN-DAAB. These resources should also help you understand in depth many issues related to the EN-DAAB.

1.      Microsoft patterns & practices Center

This link is the start page for all things related to Microsoft patterns & practices, of which the Enterprise Library is just one part.  

2.      Enterprise Library

This link is the homepage of the Enterprise Library. The current version of the Enterprise Library consists of seven application blocks, comprising Caching, Configuration, Cryptography, Data Access, Exception Handling, Logging, and Security. Do check this link for new updates to the library.

3.      Scott Densmore

Scott Densmore was one of the founders and developers of the Enterprise Library. Check his Blog for the latest updates and news on the Enterprise Library.
Conclusion
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The code download contains a single project named TestEn-DAAB. In addition, you will find the Queries.sql file which contains the code for the stored procedures used in this article. 

Last, but not least, we may summarize the Enterprise Library Data Access Application Block as providing the following features:

  1. Gives access to the most commonly used features of ADO.NET.
  2. Allows writing code that can be used by any database storage medium, with only slight changes required.
  3. Gives the opportunity to secure connection strings by encrypting the configuration settings in the application configuration file.
  4. Simplifies working with stored procedures.

In this article, I provided code samples showing how to use most of the methods of the Enterprise Library Data Access Application Block. In addition, I presented some online links, which I believe are essential to stay up to date with the latest news regarding the Enterprise Library.

Hope you enjoyed my article,

Happy Dot Netting!

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