Filling a DataSet Using an XML Template Query

Problem

You have an XML template query that you need to use from ADO.NET. You need to fill a DataSet using an XML template query.

Solution

Use an XML template query to fill a DataSet using the SQLXML Managed Classes.

The sample uses one XML file as shown in Example 8-14:

OrdersForCustomerQuery.xml

Contains the XML template query

The sample code contains two event handlers and one method:

Form.Load

Loads all Customers from Northwind into a DataTable . The default view of the DataTable is bound to the top data grid on the form. The DataGrid.CurrentCellChanged event handler is called to refresh the bottom data grid.

DataGrid.CurrentCellChanged

Gets the CustomerID for the selected row in the top data grid and calls the LoadOrderGrid( ) method to refresh the bottom grid.

LoadOrderGrid( )

This method creates a SqlXmlCommand template query and its single SqlXmlParameter object. The parameter is set to the user -specified value. A SqlXmlDataAdapter object is created and executed to fill a new DataSet based on the template query. The default view of the Orders table in the result DataSet is bound to the lower data grid on the form displaying the orders for the selected customer.

Example 8-14. File: OrdersForCustomerQuery.xml

 
 
 
 
 select
 Orders.OrderID,
 Orders.CustomerID,
 Orders.EmployeeID,
 Orders.OrderDate,
 Orders.RequiredDate,
 Orders.ShippedDate,
 Orders.ShipVia,
 Orders.Freight,
 Orders.ShipName,
 Orders.ShipAddress,
 Orders.ShipCity,
 Orders.ShipRegion,
 Orders.ShipPostalCode,
 Orders.ShipCountry,
 [Order Details].ProductID,
 [Order Details].UnitPrice,
 [Order Details].Quantity,
 [Order Details].Discount
 from
 Orders inner join [Order Details] on
 Orders.OrderID=[Order Details].OrderID
 where
 Orders.CustomerID=@CustomerID
 for xml auto
 

The C# code is shown in Example 8-15.

Example 8-15. File: UsingXmlTemplateQueriesForm.cs

// Namespaces, variables, and constants
using System;
using System.Configuration;
using System.Windows.Forms;
using Microsoft.Data.SqlXml;
using System.Data;
using System.Data.SqlClient;

private const String XMLQUERYFILENAME =
 ConfigurationSettings.AppSettings["Project_Directory"] +
 @"Chapter 08OrdersForCustomerQuery.xml";

// . . . 

private void UsingXmlTemplateQueriesForm_Load(object sender,
 System.EventArgs e)
{
 String sqlText = "SELECT * FROM Customers";

 // Load the list of customers into a table.
 SqlDataAdapter da = new SqlDataAdapter(sqlText,
 ConfigurationSettings.AppSettings["Sql_ConnectString"]);
 DataTable table = new DataTable("Customers");
 da.Fill(table);

 // Bind the default view of the table to the customer grid.
 customerDataGrid.DataSource = table.DefaultView;
 // Update orders grid based on the default row selected.
 customerDataGrid_CurrentCellChanged(null, null);
}

private void customerDataGrid_CurrentCellChanged(object sender,
 System.EventArgs e)
{
 // Retrieve the selected row from the customer grid.
 int row = customerDataGrid.CurrentRowIndex;
 // Get the customer ID.
 String customerId =
 ((DataView)customerDataGrid.DataSource).Table.
 Rows[row][0].ToString( );
 // Call method to load orders for selected customer.
 LoadOrderGrid(customerId);
}

private void LoadOrderGrid(String customerId)
{
 // Create the SQL XML command.
 SqlXmlCommand cmd = new SqlXmlCommand(
 ConfigurationSettings.AppSettings["OleDb_SqlAuth_ConnectString"]);
 cmd.CommandType = SqlXmlCommandType.TemplateFile;
 cmd.CommandText = XMLQUERYFILENAME;
 cmd.SchemaPath = XMLSCHEMAFILENAME;

 // Set the customer ID parameter for the command.
 SqlXmlParameter param = cmd.CreateParameter( );
 param.Name = "@CustomerID";
 param.Value = customerId;

 // Create the DataSet.
 DataSet ds = new DataSet( );

 // Create the SQL XML DataAdapter.
 SqlXmlAdapter da = new SqlXmlAdapter(cmd);

 // Fill the DataSet.
 try
 {
 da.Fill(ds);
 }
 catch(Exception ex)
 {
 MessageBox.Show(ex.Message);
 }

 // Bind the default view of the orders table to the orders grid.
 orderDataGrid.DataSource = ds.Tables["Orders"].DefaultView;
 orderDataGrid.CaptionText = "Orders [CustomerID: " + customerId + "]";
}

Discussion

SQLXML Managed Classes

The SQLXML Managed Classes expose SQLXML functionality from the Microsoft .NET Framework. They allow access to XML data from instance of Microsoft SQL Server 2000 or later. SQLXML Managed Classes consist of three classes:

SqlXmlCommand

Represents a command to execute against the SQL Server database.

SqlXmlParameter

Stores parameters used by the SqlXmlCommand object. The parameter is created using the CreateParameter( ) method of the SqlXmlCommand class.

SqlXmlAdapter

Links the SQLXML managed classes to the disconnected ADO.NET DataSet class.

A description of the methods and properties of these classes are shown in Tables Table 8-6 through Table 8-8.

Table 8-6 describes the methods of the SqlXmlCommand class.

Table 8-6. SqlXmlCommand methods

Method	Description
ExecuteNonQuery( )	Executes a command that does not return a result or result setfor example, an updategram or DiffGram update
ExecuteStream( )	Returns a query result set as a stream
ExecuteToStream( )	Writes query result set to an existing stream
ExecuteXmlReader( )	Returns the result set of the query as an XmlReader object
CreateParameter( )	Creates a SqlXmlParameter object used to pass parameters to a command using the Name and Value properties
ClearParameters( )	Clears SqlXmlParameter objects for a command

Table 8-7 describes the properties of the SqlXmlCommand class.

Table 8-7. SqlXmlCommand properties

Property	Description
BasePath	The directory path used when specifying a relative path for an XSL file.
ClientSideXml	Whether the conversion of the result set occurs on the client (true) or server (false). The default is false.
CommandText	The text of the command to execute.
CommandType	The type of command to execute. Takes one of the following values from the SqlXmlCommandType enumeration: DiffGram Executes a DiffGram XmlTemplate Executes an XML template TemplateFile Executes an XML template file consisting of one or more SQL or XPath queries Sql Executes a SQL command UpdateGram Executes an updategram XPath Executes an XPath command
CommandStream	The stream to execute the command from.
Namespaces	The namespace for XPath queries.
OutputEncoding	The encoding for the stream returned by the command.
RootTag	The single root-level tag for XML output returned by the command.
SchemaPath	The name of the mapping schema file and its directory path, either absolute or relative.
XslPath	The name of the XSL file and its directory path, either absolute or relative.

The SqlXmlParameter class has no methods. Table 8-8 describes the properties of the SqlXmlParameter class.

Table 8-8. SqlXmlParameter properties

Property	Description
Name	The name of the parameter for an SqlXmlCommand object
Value	The value of the parameter

The SqlXmlAdapter class has no properties. Table 8-9 describes the methods of the SqlXmlAdapter class.

Table 8-9. SqlXmlAdapter methods

Method	Description
Fill	Fills a DataSet with the XML data retrieved from the SQL Server database
Update	Updates the SQL Server database with the changes made to the DataSet

For more information about the SQLXML Managed Classes, see the Microsoft SQLXML release documentation.

Template queries

A template query is an XML document containing one or more SQL queries or stored procedures to execute. Template queries, like stored procedures, promote code reuse, facilitate security, and encourage good design by encapsulating database-specific functionality.

Parameters for the query are identified by the tag with the name attribute used to specify the parameter name and the parameter default value optionally specified between the and tags. Parameter tags are enclosed within the tags. The example shows one parameter named CustomerID without a default value:

If the CustomerID parameter had a default value of ALFKI , the parameter would be defined as follows :

ALFKI

The SQL command text must be enclosed within tags. This is shown in the example:

 select
 Orders.OrderID,
 Orders.CustomerID,

 . . . 

 [Order Details].Quantity,
 [Order Details].Discount
 from
 Orders inner join [Order Details] on
 Orders.OrderID=[Order Details].OrderID
 where
 Orders.CustomerID=@CustomerID
 for xml auto

The query is a standard SQL command with the required FOR XML clause to return the result set as XML. The query could also execute a stored procedure with the EXEC or EXECUTE command followed by the name of the stored procedure and a list of parameter values as required.

The query in the previous example has a single parameter, CustomerID , which is prepended with an @ when referred to in the query:

where Orders.CustomerID=@CustomerID