Tài liệu Formatting Column Values When Outputting Data as XML pptx

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Recipe 8.9 Formatting Column Values When Outputting Data as XML
Problem
You need to save some of the columns in a DataTable as attributes instead of elements
when you write out the data as XML.
Solution
Use the ColumnMapping property.
The sample code contains two event handlers:
Form.Load
Sets up the sample by creating a DataSet containing the first two records of the
Customers table from Northwind.
Refresh Button.Click
Iterates over all of the columns in all of the Customers tables and sets the
ColumnMapping property to the specified value. The ColumnMapping for the
ContactName column is then set to the specified value. The XML output for the
DataSet is displayed.
The C# code is shown in Example 8-13
.
Example 8-13. File: XmlElementsOrAttributesForm.cs
// Namespaces, variables, and constants
using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;

private DataSet ds;

// . . .

private void XmlElementsOrAttributesForm_Load(object sender,

System.EventArgs e)
{
ds = new DataSet("CustomersDataSet");

// Get the top two rows from the Customers table.
SqlDataAdapter da = new SqlDataAdapter(
"SELECT TOP 2 * FROM Customers",
ConfigurationSettings.AppSettings["Sql_ConnectString"]);
da.Fill(ds, "Customers");
}

private void refreshButton_Click(object sender, System.EventArgs e)
{
// Set the mapping type for each column in the table.
foreach(DataTable table in ds.Tables)
foreach(DataColumn column in table.Columns)
{
if(tableAttributeRadioButton.Checked)
column.ColumnMapping = MappingType.Attribute;
else if(tableElementRadioButton.Checked)
column.ColumnMapping = MappingType.Element;
else if(tableHiddenRadioButton.Checked)
column.ColumnMapping = MappingType.Hidden;
}

// Set the mapping type for the ContactName column.
DataColumn dc = ds.Tables["Customers"].Columns["ContactName"];
if(columnAttributeRadioButton.Checked)
dc.ColumnMapping = MappingType.Attribute;
else if(columnElementRadioButton.Checked)

dc.ColumnMapping = MappingType.Element;
else if(columnHiddenRadioButton.Checked)
dc.ColumnMapping = MappingType.Hidden;
else if(columnSimpleContentRadioButton.Checked)
dc.ColumnMapping = MappingType.SimpleContent;

// Display the XML.
xmlTextBox.Text = ds.GetXml( );
}
Discussion
The ColumnMapping property of the DataColumn specifies how the value of a column
will be written when the DataSet is output as an XML document with the GetXml( )
method or WriteXml( ) method. The property value is one of the MappingType
enumeration values described in Table 8-5.
Table 8-5. MappingType enumeration
Value Description
Attribute
The value is written as an XML attribute. For example:
<MyRow>
<MyColumn>my column value</MyColumn>
</MyRow>
Element
The value is written as an XML element. For example:
<MyRow MyColumn="my column value" />
This is the default.
Hidden The value is not written in the XML output.
SimpleContent
The value is written as text in the XML element for its row. For
example:
<MyRow>my column value</MyRow>

This value can only be used if the table has neither Element columns
nor nested relations.
There is no way to set the ColumnMapping property for all columns in a DataTable or
DataSet at once. Each column must be set individually.
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