Tài liệu Filling a DataSet Using an XML Template Query ppt

Solution Use an XML template query to fill a DataSet using the SQLXML Managed Classes.. LoadOrderGrid This method creates a SqlXmlCommand template query and its single SqlXmlParameter

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Recipe 8.10 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

<?xml version="1.0" encoding="utf-8" ?>

<ROOT xmlns:sql='urn:schemas-microsoft-com:xml-sql'> <sql:header>

<sql:param name="CustomerID" />

</sql:header>

<sql:query>

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

</sql:query>

</ROOT>

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 08\OrdersForCustomerQuery.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 set—

for 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 <sql:param> tag with the name attribute used to specify the parameter name and the parameter default value optionally specified between the <sql:param> and <sql:param> tags Parameter tags are enclosed within the

<sql:header> tags The example shows one parameter named CustomerID without a

default value:

<sql:header>

<sql:param name="CustomerID" />

</sql:header>

If the CustomerID parameter had a default value of ALFKI, the parameter would be

defined as follows:

<sql:param name="CustomerID">ALFKI</sql:param>

The SQL command text must be enclosed within <sql:query> tags This is shown in the example:

<sql:query>

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

</sql:query>

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

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