Tài liệu Saving and Loading a DataSet from XML pptx

The sample code contains three event handlers: Write Button.Click Creates a DataSet containing the Orders and Order Details tables from Northwind and a relation between the two tables..

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[ Team LiB ]

Recipe 8.2 Saving and Loading a DataSet from XML

Problem

You need to save a DataSet as an XML file and create a DataSet from an XML file

Solution

Use the XmlTextWriter and XmlTextReader classes

The sample code contains three event handlers:

Write Button.Click

Creates a DataSet containing the Orders and Order Details tables from Northwind and a relation between the two tables The XML schema and data for the DataSet

is written both to a file and to a text box on the form

Read Button.Click

Creates a DataSet and reads in schema and data from a file containing a previously serialized XML The XML is written from the DataSet to a stream and displayed Clear Button.Click

Clears the data grid and the result text box

The C# code is shown in Example 8-3

Example 8-3 File: XmlFileForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Windows.Forms;

using System.Text;

using System.IO;

using System.Xml;

using System.Xml.Schema;

using System.Data;

using System.Data.SqlClient;

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// Table name constants

private const String ORDERS_TABLE = "Orders";

private const String ORDERDETAILS_TABLE = "OrderDetails";

// Relation name constants

private const String ORDERS_ORDERDETAILS_RELATION =

"Orders_OrderDetails_Relation";

// Field name constants

private const String ORDERID_FIELD = "OrderID";

//

private void writeXmlButton_Click(object sender, System.EventArgs e)

{

DataSet ds = new DataSet( );

SqlDataAdapter da;

// Fill the Order table and add it to the DataSet

da = new SqlDataAdapter("SELECT * FROM Orders",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable orderTable = new DataTable(ORDERS_TABLE);

da.FillSchema(orderTable, SchemaType.Source);

da.Fill(orderTable);

ds.Tables.Add(orderTable);

// Fill the OrderDetails table and add it to the DataSet

da = new SqlDataAdapter("SELECT * FROM [Order Details]",

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

DataTable orderDetailTable = new DataTable(ORDERDETAILS_TABLE); da.FillSchema(orderDetailTable, SchemaType.Source);

da.Fill(orderDetailTable);

ds.Tables.Add(orderDetailTable);

// Create a relation between the tables

ds.Relations.Add(ORDERS_ORDERDETAILS_RELATION,

ds.Tables[ORDERS_TABLE].Columns[ORDERID_FIELD],

ds.Tables[ORDERDETAILS_TABLE].Columns[ORDERID_FIELD], true);

// Bind the default view of the Orders table to the grid

resultDataGrid.DataSource = ds.Tables[ORDERS_TABLE].DefaultView;

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// Write the XSD schema and data to a file

// Display file dialog to select XML file to write

SaveFileDialog sfd = new SaveFileDialog( );

sfd.InitialDirectory = System.IO.Path.GetTempPath( );

sfd.Filter = "XML Files (*.xml)|*.xml|All files (*.*)|*.*";

sfd.FilterIndex = 1;

if (sfd.ShowDialog( ) == DialogResult.OK)

{

FileStream fs = new FileStream(sfd.FileName, FileMode.Create, FileAccess.Write);

// Create an XmlTextWriter using the file stream

XmlTextWriter xtw = new XmlTextWriter(fs, Encoding.Unicode);

try

{

// Write the XML to the file

ds.WriteXml(xtw, XmlWriteMode.WriteSchema);

resultTextBox.Text = "XML file written.";

}

catch(Exception ex)

{

MessageBox.Show(ex.Message);

}

finally

{

xtw.Close( );

}

private void readXmlButton_Click(object sender, System.EventArgs e) {

// Write the XML schema from a file

// Display file dialog to select XML file to read

OpenFileDialog ofd = new OpenFileDialog( );

ofd.InitialDirectory = System.IO.Path.GetTempPath( );

ofd.Filter = "XML Files (*.xml)|*.xml|All files (*.*)|*.*";

ofd.FilterIndex = 1;

if (ofd.ShowDialog( ) == DialogResult.OK)

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{

FileStream fs = new FileStream(ofd.FileName, FileMode.Open, FileAccess.Read);

// Create an XmlTextReader using the file stream

XmlTextReader xtr = new XmlTextReader(fs);

try

{

// Read the schema into the DataSet

DataSet ds = new DataSet( );

ds.ReadXml(xtr, XmlReadMode.ReadSchema);

// Bind the default view of the Orders table to the grid

resultDataGrid.DataSource =

ds.Tables[ORDERS_TABLE].DefaultView;

// Write the XML to a memory stream and display it

MemoryStream ms = new MemoryStream( );

ds.WriteXml(ms, XmlWriteMode.WriteSchema);

byte[] result = ms.ToArray( );

ms.Close( );

resultTextBox.Text = Encoding.UTF8.GetString(result, 0, result.Length);

}

catch(Exception ex)

{

MessageBox.Show(ex.Message);

}

finally

{

xtr.Close( );

}

private void clearButton_Click(object sender, System.EventArgs e) {

// Clear the data grid and the result text box

resultDataGrid.DataSource = null;

resultTextBox.Clear( );

}

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Discussion

The solution uses the XmlTextWriter and XmlTextReader classes to write and read the

XML data for the DataSet For more information about these classes, see the Discussion for Recipe 8.1 and the MSDN Library

The WriteXml( ) and ReadXml( ) methods of the DataSet are used to write and read the XML for the DataSet The WriteXml( ) method takes an optional argument that specifies

a value from the XmlWriteMode enumeration described in Table 8-2

Table 8-2 XmlWriteMode enumeration Value Description

DiffGram

The DataSet is written as a DiffGram, which is an XML format used by .NET to persist and serialize a DataSet A DiffGram includes all

information required to recreate the DataSet including original and current values, row errors, and row order A DiffGram does not include information about the DataSet schema

IgnoreSchema The DataSet is written without inline schema information This is the

default

WriteSchema The DataSet is written with an inline XSD schema for the relational

structure of the DataSet

If an in-line schema is not written, the ReadXml( ) method can still be used to read the

data into a DataSet, but the method will not be able to completely recreate the schema for the DataSet

The XmlRead( ) method takes an optional argument that specifies a value from the

XmlReadMode enumeration described in Table 8-3

Table 8-3 XmlReadMode enumeration Value Description

Auto

Uses the most appropriate of the following settings:

• DiffGram if the data is a DiffGram

• ReadSchema if the DataSet already has a schema or the XML document contains an inline schema

• InferSchema if the DataSet does not already have a schema and

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the XML document does not contain an inline schema Auto is the default

DiffGram

Reads a DiffGram applying the changes to the DataSet The target DataSet must have the same schema as the DataSet from which the WriteXml( ) method created the DiffGram Otherwise, an exception is raised

Fragment Reads an XML document such as one generated by queries with the

FOR XML clause

IgnoreSchema

Ignores any inline schema and reads data from the XML document into the existing DataSet schema Data not matching the existing schema is discarded

InferSchema

Ignores any inline schema, infers the schema from the data, and loads the data into the DataSet The DataSet schema is extended by adding new tables and columns as required

ReadSchema

Reads any inline schema and loads the data into the DataSet If the DataSet already contains tables, new tables will be added but an exception will be raised if any tables defined by the inline schema already exist in the DataSet

Example 8-4 shows the XML file with inline schema written by this solution

Example 8-4 Orders with order details XML file, with schema

<xs:schema id="NewDataSet" xmlns=""

xmlns:xs="http://www.w3.org/2001/XMLSchema"

xmlns:msdata="urn:schemas-microsoft-com:xml-msdata"><

<xs:element name="NewDataSet" msdata:IsDataSet="true">

<xs:complexType>

<xs:choice maxOccurs="unbounded">

<xs:element name="Orders">

<xs:complexType>

<xs:sequence>

<xs:element name="OrderID" msdata:ReadOnly="true"

msdata:AutoIncrement="true" type="xs:int" />

<xs:element name="CustomerID" minOccurs="0">

<xs:simpleType>

<xs:restriction base="xs:string">

<xs:maxLength value="5" />

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</xs:restriction>

</xs:simpleType>

</xs:element>

<xs:element name="EmployeeID" type="xs:int"

minOccurs="0" />

<xs:element name="OrderDate" type="xs:dateTime" minOccurs="0" />

<xs:element name="RequiredDate" type="xs:dateTime" minOccurs="0" />

<xs:element name="ShippedDate" type="xs:dateTime" minOccurs="0" />

<xs:element name="ShipVia" type="xs:int"

minOccurs="0" />

<xs:element name="Freight" type="xs:decimal"

minOccurs="0" />

<xs:element name="ShipName" minOccurs="0"> <xs:simpleType>

</xs:restriction>

</xs:simpleType>

</xs:element>

<xs:element name="ShipAddress" minOccurs="0"> <xs:simpleType>

</xs:restriction>

</xs:simpleType>

</xs:element>

<xs:element name="ShipCity" minOccurs="0">

<xs:simpleType>

</xs:restriction>

</xs:simpleType>

</xs:element>

<xs:element name="ShipRegion" minOccurs="0"> <xs:simpleType>

</xs:restriction>

</xs:simpleType>

</xs:element>

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<xs:element name="ShipPostalCode" minOccurs="0">

<xs:simpleType>

</xs:restriction>

</xs:simpleType>

</xs:element>

<xs:element name="ShipCountry" minOccurs="0">

<xs:simpleType>

</xs:restriction>

</xs:simpleType>

</xs:element>

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:element name="OrderDetails">

<xs:complexType>

<xs:sequence>

<xs:element name="OrderID" type="xs:int" />

<xs:element name="ProductID" type="xs:int" />

<xs:element name="UnitPrice" type="xs:decimal" />

<xs:element name="Quantity" type="xs:short" />

<xs:element name="Discount" type="xs:float" />

</xs:sequence>

</xs:complexType>

</xs:element>

</xs:choice>

</xs:complexType>

<xs:unique name="Constraint1" msdata:PrimaryKey="true">

<xs:selector xpath=".//Orders" />

<xs:field xpath="OrderID" />

</xs:unique>

<xs:unique name="OrderDetails_Constraint1"

msdata:ConstraintName="Constraint1" msdata:PrimaryKey="true"> <xs:selector xpath=".//OrderDetails" />

<xs:field xpath="ProductID" />

</xs:unique>

<xs:keyref name="Orders_OrderDetails_Relation" refer="Constraint1"> <xs:selector xpath=".//OrderDetails" />

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</xs:keyref>

</xs:element>

</xs:schema>

<CustomerID>VINET</CustomerID>

<ShipName>Vins et alcools Chevalier</ShipName>

<ShipAddress>59 rue de l'Abbaye</ShipAddress>

<ShipCity>Reims</ShipCity>

<ShipCountry>France</ShipCountry>

</Orders>

<CustomerID>TOMSP</CustomerID>

<ShipName>Toms Spezialitäten</ShipName>

<ShipAddress>Luisenstr 48</ShipAddress>

<ShipCity>Münster</ShipCity>

<ShipCountry>Germany</ShipCountry>

</Orders>

<! >

<CustomerID>BONAP</CustomerID>

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<ShipAddress>12, rue des Bouchers</ShipAddress>

<ShipCity>Marseille</ShipCity>

<ShipCountry>France</ShipCountry>

</Orders>

<CustomerID>RATTC</CustomerID>

<ShipName>Rattlesnake Canyon Grocery</ShipName>

<ShipAddress>2817 Milton Dr.</ShipAddress>

<ShipCity>Albuquerque</ShipCity>

</Orders>

</OrderDetails>

</OrderDetails>

<! >

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Tiêu đề	Saving and Loading a DataSet from XML
Tác giả	Team LiB
Thể loại	Recipe