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Building ASP.NET Applications with Delphi and Advantage Database Server : Page 3

The Advantage Data Provider for .NET provides a feature-rich mechanism for Delphi developers using the Advantage Database Server (ADS) to build ASP.NET web applications and web services.


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Loading Data Programmatically

While the preceding example used data binding, you could achieve the same effect by loading the list box programmatically, by iterating through the DataReader and loading each row into the list box manually. The following example has exactly the same results as the preceding example, but without the call to DataBind.

procedure TUseDataReader.Button2_Click( sender: System.Object; e: System.EventArgs); var ReusableDataLayer1: ReusableDataLayer; DataReader: AdsDataReader; begin ReusableDataLayer1 := ReusableDataLayer.Create(Context); try DataReader := ReusableDataLayer1.GetAllEmployeeNames; try while DataReader.Read do ListBox1.Items.Add( ListItem.Create(DataReader.GetString(0), DataReader.GetInt32(1).ToString)); finally DataReader.Close end; finally ReusableDataLayer1.Dispose; end; end;



You use DataTables to hold part or all of a result set in memory: for data manipulation, data binding, and even storing sets of data for later use. One of the easiest ways to populate a DataTable is to use an AdsDataAdapter. An AdsDataAdapter contains an AdsCommand that returns a result set, either through a SQL SELECT statement or a call to a stored procedure that returns a result set. After configuring the AdsDataAdapter, you call its Fill method to transfer the data into a DataTable, as shown below:

function ReusableDataLayer.GetCustomerSales(CustNo: Integer):DataTable; var Command: AdsCommand; Parameter: AdsParameter; DataAdapter: AdsDataAdapter; begin Command := Connection.CreateCommand; Command.CommandText := 'SELECT * FROM INVOICE ' + ' WHERE [Customer ID] = :custno'; Parameter := Command.CreateParameter; Parameter.DbType := System.Data.DbType.Int32; Parameter.ParameterName := 'custno'; Parameter.Value := TObject(CustNo); Command.Parameters.Add(Parameter); DataAdapter := AdsDataAdapter.Create(Command); Result := DataTable.Create; DataAdapter.Fill(Result); end;

The GetCustomerSales method returns a DataTable. Note that the example also demonstrates using an AdsParameter.

The following code uses the GetCustomerSales method defined above. It obtains the value passed to GetCustomerSales from a TextBox on a web page:

procedure TDataTable.Button1_Click( sender: System.Object; e: System.EventArgs); var ReusableDataLayer1: ReusableDataLayer; DataReader: AdsDataReader; begin ReusableDataLayer1 := ReusableDataLayer.Create(Context); try DataGrid1.DataSource := ReusableDataLayer1.GetCustomerSales( Convert.ToInt32(TextBox1.Text)); DataBind; finally ReusableDataLayer1.Dispose; end; end;

 
Figure 7. DataGrid Example: This DataGrid was populated using an AdsDataAdapter that retrieves invoices for a specific Customer ID.

Figure 7 shows an example of how the web page might look after the preceding code executes.

The final example demonstrates the use of an AdsExtendedReader (see Listing 1). As mentioned earlier in this paper, the AdsExtendedReader is unique in the world of .NET data providers, in that it supports both bi-directional navigation and read/write capabilities.

To recreate the code in Listing 1 without using an AdsExtendedReader, you would have to construct a separate UPDATE query to update the first record modified by this example, as well as a SELECT query (to detect if the second record already exists) followed by an INSERT query.

The value of the AdsExtendedReader in ASP.NET applications cannot be overemphasized; it gives you an alternative that—in some cases—can save you from writing dozens, if not hundreds of lines of code.

The Advantage Data Provider for .NET is the preferred data access mechanism for developing ASP.NET applications with Delphi and the Advantage Database Server. It's easy to use and deploy, and supports some advanced features unavailable in any other .NET data provider.



Cary Jensen is president of Jensen Data Systems, Inc., a Texas-based company that specializes in Internet and database development, training, and consulting. He is an authority on database development, an award-winning, best-selling author of 20 books, and an author and speaker for Advantage Developer Days and Delphi Developer Days seminars. He speaks widely at conferences, workshops, and training seminars throughout North America and Europe. Cary holds a Ph.D. from Rice University in Human Factors Psychology, specializing in human-computer interaction. Check out his web site for more information.
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