Tài liệu Writing and Reading XML Using a DataSet Object ppt

You can write out the contents of the DataTable objects contained in a DataSet to an XML file using the WriteXml method.. You can write out the schema of a DataSet object to an XML file

Writing and Reading XML Using a DataSet Object

XML is a convenient format for moving information around You can write out the

contents of the DataTable objects contained in a DataSet to an XML file using the

WriteXml() method The XML file written by this method contains the DataTable

column names and values

You can write out the schema of a DataSet object to an XML file using the

WriteXmlSchema() method The XML file written by this method contains the structure

of the DataTable objects contained in the DataSet You can also get the XML in a

DataSet using the GetXml() method, which returns the XML in a string

You can read the contents of the DataTable objects in an XML file into a DataSet using the ReadXml() method You can also read the schema contained in an XML file using the ReadXmlSchema() method

Note SQL Server also contains extensive built-in XML functionality, which you'll learn

Using the WriteXml() Method

Let's say you have a DataSet object named myDataSet Assume that myDataSet has a DataTable that contains the CustomerID, CompanyName, ContactName, and Address columns for the top two rows from the Customers table The following code shows this: SqlCommand mySqlCommand = mySqlConnection.CreateCommand();

mySqlCommand.CommandText =

"SELECT TOP 2 CustomerID, CompanyName, ContactName, Address " +

"FROM Customers " +

"ORDER BY CustomerID";

SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter();

mySqlDataAdapter.SelectCommand = mySqlCommand;

DataSet myDataSet = new DataSet();

mySqlConnection.Open();

Console.WriteLine("Retrieving rows from the Customers table");

mySqlDataAdapter.Fill(myDataSet, "Customers");

mySqlConnection.Close();

You can write out the contents of myDataSet to an XML file using the WriteXml()

method For example:

myDataSet.WriteXml("myXmlFile.xml");

This writes an XML file named myXmlFile.xml, as shown in Listing 10.9

Listing 10.9: MYXMLFILE.XML

<?xml version="1.0" standalone="yes"?>

<NewDataSet>

<Customers>

<CustomerID>ALFKI</CustomerID>

<CompanyName>Alfreds Futterkiste</CompanyName>

<ContactName>Maria Anders</ContactName>

<Address>Obere Str 57</Address>

</Customers>

<Customers>

<CustomerID>ANATR</CustomerID>

<CompanyName>Ana Trujillo Emparedados y helados</CompanyName>

<ContactName>Ana Trujillo</ContactName>

<Address>Avda de la Constitución 2222</Address>

</Customers>

</NewDataSet>

As you can see, this file contains the columns for the rows retrieved from the Customers table

The WriteXml() method is overloaded as follows:

void WriteXml(Stream myStream);

void WriteXml(string fileName);

void WriteXml(TextWriter myTextWriter);

void WriteXml(XmlWriter myXmlWriter);

void WriteXml(stream myStream, XmlWriteMode myXmlWriteMode);

void WriteXml(string fileName, XmlWriteMode myXmlWriteMode);

void WriteXml(TextWriter myTextWriter, XmlWriteMode myXmlWriteMode);

void WriteXml(XmlWriter myXmlWriter, XmlWriteMode myXmlWriteMode);

where myXmlWriteMode is a constant from the System.Data.XmlWriteMode

constants defined in the XmlWriteMode enumeration

Table 10.8: XmlWriteMode ENUMERATION MEMBERS

CONSTANT DESCRIPTION

Table 10.8: XmlWriteMode ENUMERATION MEMBERS

CONSTANT DESCRIPTION

and the changes to those values to make them current You can generate a DiffGram that contains only the changes by calling the GetChanges() method of your DataSet, and then call WriteXml()

IgnoreSchema Writes out only the data in the DataSet, without writing the schema

IgnoreSchema is the default

WriteSchema Writes out the schema in the DataSet

The following example shows the use of the XmlWriteMode.WriteSchema constant: myDataSet.WriteXml("myXmlFile2.xml", XmlWriteMode.WriteSchema);

Listing 10.10: MYXMLFILE2.XML

<?xml version="1.0" standalone="yes"?>

<NewDataSet>

<xsd:schema id="NewDataSet" targetNamespace="" xmlns=""

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

xmlns:msdata="urn:schemas-microsoft-

com:xml-msdata">

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

<xsd:complexType>

<xsd:choice maxOccurs="unbounded">

<xsd:element name="Customers">

<xsd:complexType>

<xsd:sequence>

<xsd:element name="CustomerID" type="xsd:string" minOccurs="0" />

<xsd:element name="CompanyName" type="xsd:string" minOccurs="0" /> <xsd:element name="ContactName" type="xsd:string" minOccurs="0" /> <xsd:element name="Address" type="xsd:string" minOccurs="0" />

</xsd:sequence>

</xsd:complexType>

</xsd:element>

</xsd:choice>

</xsd:complexType>

</xsd:element>

</xsd:schema>

<Customers>

<CustomerID>ALFKI</CustomerID>

<CompanyName>Alfreds Futterkiste</CompanyName>

<ContactName>Maria Anders</ContactName>

<Address>Obere Str 57</Address>

</Customers>

<Customers>

<CustomerID>ANATR</CustomerID>

<CompanyName>Ana Trujillo3 Emparedados y helados</CompanyName>

<ContactName>Ana Trujillo</ContactName>

<Address>Avda de la Constitución 2222</Address>

</Customers>

</NewDataSet>

As you can see, this file contains the schema definition for the columns used in the

original SELECT statement, as well as the column values for the rows retrieved

Using the WriteXmlSchema() Method

You can write out the schema of myDataSet to an XML file using the WriteXmlSchema() method For example:

myDataSet.WriteXmlSchema("myXmlSchemaFile.xml");

Listing 10.11: MYXMLSCHEMAFILE.XML

<?xml version="1.0" standalone="yes"?>

<xsd:schema id="NewDataSet" targetNamespace="" xmlns=""

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

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

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

<xsd:complexType>

<xsd:choice maxOccurs="unbounded">

<xsd:element name="Customers">

<xsd:complexType>

<xsd:sequence>

<xsd:element name="CustomerID" type="xsd:string" minOccurs="0" />

<xsd:element name="CompanyName" type="xsd:string" minOccurs="0" /> <xsd:element name="ContactName" type="xsd:string" minOccurs="0" />

<xsd:element name="Address" type="xsd:string" minOccurs="0" />

</xsd:sequence>

</xsd:complexType>

</xsd:element>

</xsd:choice>

</xsd:complexType>

</xsd:element>

</xsd:schema>

As you can see, this file contains the schema definition for the columns retrieved from the Customers table by the original SELECT statement

Using the ReadXml() Method

You can read the contents of an XML file into a DataSet object using the ReadXml() method This method reads the rows and columns from the XML file into DataTable objects of the DataSet For example, the following statement uses the ReadXml() method

to read the XML file myXmlFile.xml previously written by the WriteXml() method: myDataSet.ReadXml("myXmlFile.xml");

The ReadXml() method is overloaded as follows:

void ReadXml(Stream myStream);

void ReadXml(string fileName);

void ReadXml(TextReader myTextReader);

void ReadXml(XmlReader myXmlReader);

void ReadXml(stream myStream, XmlReadMode myXmlReadMode);

void ReadXml(string fileName, XmlReadMode myXmlReadMode);

void ReadXml(TextReader myTextReader, XmlReadMode myXmlReadMode);

void ReadXml(XmlReader myXmlReader, XmlReadMode myXmlReadMode);

where myXmlReadMode is a constant from the System.Data.XmlReadMode enumeration

defined in the XmlReadMode enumeration

Table 10.9: XmlReadMode ENUMERATION MEMBERS

CONSTANT DESCRIPTION

DiffGram

a schema, then XmlReadMode is set to ReadSchema

Table 10.9: XmlReadMode ENUMERATION MEMBERS

CONSTANT DESCRIPTION

contain a schema, then XmlReadMode is set to InferSchema Auto is the default

and the changes to those values to make them current The changes are then applied to your DataSet This is similar to calling the Merge() method of a DataSet in that changes from one DataSet are merged with another

those generated by executing SELECT statements containing FOR XML clauses

IgnoreSchema Reads out only the data in the DataSet, without reading the schema InferSchema Infers the schema of the XML file by examining the data stored in it ReadSchema Reads the schema from the XML file into the DataSet

The following example shows the use of the XmlReadMode.ReadSchema constant: myDataSet.ReadXml("myXmlFile2.xml", XmlReadMode.ReadSchema);

Listing 10.12 illustrates how to write and read XML files using ADO.NET

Listing 10.12: WRITEANDREADXML.CS

/*

WriteAndReadXml.cs illustrates how to write and read XML files

*/

using System;

using System.Data;

using System.Data.SqlClient;

class WriteAndReadXML

{

public static void Main()

{

SqlConnection mySqlConnection =

new SqlConnection(

"server=localhost;database=Northwind;uid=sa;pwd=sa"

);

SqlCommand mySqlCommand = mySqlConnection.CreateCommand();

mySqlCommand.CommandText =

"SELECT TOP 2 CustomerID, CompanyName, ContactName, Address " + "FROM Customers " +

"ORDER BY CustomerID";

SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter();

mySqlDataAdapter.SelectCommand = mySqlCommand;

DataSet myDataSet = new DataSet();

mySqlConnection.Open();

Console.WriteLine("Retrieving rows from the Customers table");

mySqlDataAdapter.Fill(myDataSet, "Customers");

mySqlConnection.Close();

// use the WriteXml() method to write the DataSet out to an

// XML file

Console.WriteLine("Writing rows out to an XML file named " +

"myXmlFile.xml using the WriteXml() method");

myDataSet.WriteXml("myXmlFile.xml");

Console.WriteLine("Writing schema out to an XML file named " +

"myXmlFile2.xml using the WriteXml() method");

myDataSet.WriteXml("myXmlFile2.xml", XmlWriteMode.WriteSchema);

// use the WriteXmlSchema() method to write the schema of the

// DataSet out to an XML file

Console.WriteLine("Writing schema out to an XML file named " +

"myXmlSchemaFile.xml using the WriteXmlSchema() method");

myDataSet.WriteXmlSchema("myXmlSchemaFile.xml");

// use the Clear() method to clear the current rows in the DataSet

myDataSet.Clear();

// use the ReadXml() method to read the contents of the XML file

// into the DataSet

Console.WriteLine("Reading rows from myXmlFile.xml " +

"using the ReadXml() method");

myDataSet.ReadXml("myXmlFile.xml");

DataTable myDataTable = myDataSet.Tables["Customers"];

foreach (DataRow myDataRow in myDataTable.Rows)

{

Console.WriteLine("CustomerID = " + myDataRow["CustomerID"]);

Console.WriteLine("CompanyName = " + myDataRow["CompanyName"]);

Console.WriteLine("ContactName = " + myDataRow["ContactName"]); Console.WriteLine("Address = " + myDataRow["Address"]);

}

}

}

The output from this program is as follows:

Retrieving rows from the Customers table

Writing rows out to an XML file named myXmlFile.xml using

the WriteXml() method

Writing schema out to an XML file named myXmlFile2.xml

using the WriteXml() method

Writing schema out to an XML file named myXmlSchemaFile.xml

using the WriteXmlSchema() method

Reading rows from myXmlFile.xml using the ReadXml() method

CustomerID = ALFKI

CompanyName = Alfreds Futterkiste

ContactName = Maria Anders

Address = Obere Str 57

CustomerID = ANATR

CompanyName = Ana Trujillo3 Emparedados y helados

ContactName = Ana Trujillo

Address = Avda de la Constitución 2222