The Attributes of an XML Element
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The Attributes of an XML Element |
Fundamentals of Attributes
Introduction
When studying XML elements we saw how they constituted the main objects of an XML document. We also saw that an element could be nested inside of another element. Instead of nesting an element, you can make the nested element be the nesting element and thereby giving away its element qualities. This is the basis of an attribute.
An attribute is a value that is created as part of an element, making that value different from the value of a regular element. There are similarities and differences between an element and an attribute.
The element and the attribute have these in common:
The differences between an element and an attribute are:
To support attributes, the .NET Framework provides a class named XmlAttribute that is derived from XmlNode:
Public Class XmlAttribute Inherits XmlNode
Manually Creating an Attribute
Imagine you have an element, named street-address as a child of another element as follows:
<?xml version="1.0" encoding="utf-8"?>
<metro-system>
<station>
<street-address>15903 Somerville Drive</street-address>
</station>
</metro-system>
An attribute must be created inside the start-tag of an element. To manually create an attribute, type the left angle bracket of the element, followed by the name of the element, an empty space, and the name of the attribute. The name follows the same rules we defined for names in XML.
An attribute should have a value that can be used to distinguish it. To specify the name of an attribute, assign a value as a string to its name. In the case of the above code fragment, since street-address is simply a child of the station element, you can change the street-address element to become an attribute of the station element as follows:
<?xml version="1.0" encoding="utf-8"?>
<metro-system>
<station street-address="15903 Somerville Drive"></station>
</metro-system>
Now, street-address is an attribute of the station element.
The Collection of Attributes of an Element
Introduction
An element can have many different attributes. Here is an example:
<?xml version="1.0" encoding="utf-8"?> <metro-system> <station street-address="15903 Somerville Drive" city="Rockville" state="MD" ZipCode=20855> <identity>2014</identity> <name>Shady Grove</name> <line> <color>Red</color> </line> <daily-parking>1</daily-parking> <metered-parking>1</metered-parking> </station> <station street-address="192 19th St. SE" city="Washington" state="DC" ZipCode=20003 parking="None" car-sharing="None"> <identity>8640</identity> <name>Stadium-Armory</name> <line> <color>Orange</color> <color>Blue</color> <color>Silver</color> </line> <daily-parking>0</daily-parking> <metered-parking>0</metered-parking> </station> </metro-system>
The attributes of an element are stored in a collection named XmlAttributeCollection. To support attributes, the XmlElement class is equipped with a property named Attributes:
Public Overrides ReadOnly Property Attributes As XmlAttributeCollection
Here is an example of starting to access the attributes of an element:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Metro System - Stations</title>
</head>
<body>
<h3>Metro System - Stations</h3>
<%
Dim i As Integer
Dim xaStation As XmlAttribute
Dim xnlStations As XmlNodeList
Dim xdStations As New XmlDocument()
Dim strMetroFile = Server.MapPath("metro-system.xml")
If File.Exists(strMetroFile) Then
Using fsStations As New FileStream(strMetroFile, FileMode.Open, FileAccess.Read)
xdStations.Load(fsStations)
xnlStations = xdStations.GetElementsByTagName("station")
For i = 0 To xnlStations.Count - 1
For Each xaStation In xnlStations(i).Attributes
. . .
Next
Next
End Using
End If
%>
</body>
</html>
The Number of Attributes in an Element
To know the number of attributes in an element, you can use the XmlNamedNodeMap.Count property:
Public Overridable ReadOnly Property Count As Integer
Accessing an XML Attribute
To access an attribute by its position in the collection, you can use the XmlNamedNodeMap.Item() method:
Public Overridable Function Item(ByVal index As Integer) As XmlNode
The XmlAttributeCollection class is equipped with an ItemOf indexed property. This property is overloaded in three versions. The first version has the following syntax:
Public ReadOnly Property ItemOf(ByVal i As Integer) As XmlAttribute
This property allows you to access an attribute by considering that the attributes are stored in an array. The first or most left attribute has an index of 0; the second attribute from left (of course without counting the name of the element) has an index of 1, and so on.
It can be difficult and sometimes unpredictable, in some scenarios, to access an attribute by its index because you must know exactly where each attribute is positioned. Consider the following version of our Videos.xml XML file:
<?xml version="1.0" encoding="utf-8" ?>
<videos FileDesc="Personal Video Collection">
<video ISBN="0-7888-1623-3"
ScreenRatio="Standard"
SoundtrackAvailable="True">
<title StoryBy="Marty Kaplan and Jonathan Reynold"
Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
<director>Jonathan Lynn</director>
<actors></actors>
<length>112 Minutes</length>
<format>DVD</format>
<rating>R</rating>
</video>
<video ISBN="0-7907-3900-3">
<title Screenplay="Charlie Peter">Her Alibi</title>
<director>Bruce Beresford</director>
<length>94 Mins</length>
<format>DVD</format>
<rating>PG-13</rating>
</video>
</videos>
In the first video, the name of the screenplay writer is stored at index 1. In the second video, the name of the screenplay writer is stored at index 0. In this case, it may not be a good idea to use the index to locate an attribute. Fortunately, the second version of the overloaded XmlAttributeCollection.ItemOf() property has the following syntax:
Public ReadOnly Property ItemOf(ByVal name As String) As XmlAttribute
With this version, you can explicitly specify the name of the attribute you want.
The Name of an Attribute
In the .NET Framework, an attribute is represented by the XmlAttribute class. Like all XML objects, this class is based on the XmlNode class. The name of an attribute is represented by its (read-only) Name property. Here is an example of accessing them:
Metro System: stations.xml
<?xml version="1.0" encoding="utf-8" ?>
<metro-system>
<station street-address="15903 Somerville Drive"
city="Rockville" state="MD" ZipCode="20855">
<identity>2014</identity>
<name>Shady Grove</name>
<line>
<color>Red</color>
</line>
<daily-parking>1</daily-parking>
<metered-parking>1</metered-parking>
</station>
<station street-address="192 19th St. SE"
city="Washington" state="DC" ZipCode="20003"
parking="None"
car-sharing="None">
<identity>8640</identity>
<name>Stadium-Armory</name>
<line>
<color>Orange</color>
<color>Blue</color>
<color>Silver</color>
</line>
<daily-parking>0</daily-parking>
<metered-parking>0</metered-parking>
</station>
</metro-system>
Metro System: stations.aspx
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Metro System - Stations</title>
</head>
<body>
<h3>Metro System - Stations</h3>
<%
Dim i As Integer
Dim xaStation As XmlAttribute
Dim xnlStations As XmlNodeList
Dim xdStations As New XmlDocument()
Dim strMetroFile = Server.MapPath("App_Data/stations.xml")
If File.Exists(strMetroFile) Then
Using fsStations As New FileStream(strMetroFile, FileMode.Open, FileAccess.Read)
xdStations.Load(fsStations)
xnlStations = xdStations.GetElementsByTagName("station")
For i = 0 To xnlStations.Count - 1
For Each xaStation In xnlStations(i).Attributes
Response.Write("<br>" & xaStation.Name)
Next
Next
End Using
End If
%>
</body>
</html>
This would produce:
The Inner Text of an Attribute
The value of an attribute is represented by its Value property. Here is an example of accessing the values of attributes:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Metro System - Stations</title>
</head>
<body>
<h3>Metro System - Stations</h3>
<%
Dim i As Integer
Dim xaStation As XmlAttribute
Dim xnlStations As XmlNodeList
Dim xdStations As New XmlDocument()
Dim strMetroFile = Server.MapPath("App_Data/stations.xml")
If File.Exists(strMetroFile) Then
Using fsStations As New FileStream(strMetroFile, FileMode.Open, FileAccess.Read)
xdStations.Load(fsStations)
xnlStations = xdStations.GetElementsByTagName("station")
For i = 0 To xnlStations.Count - 1
For Each xaStation In xnlStations(i).Attributes
Response.Write("<br>" & xaStation.Value)
Next
Next
End Using
End If
%>
</body>
</html>
This would produce:
The Inner Text and Inner Xml of an Attribute
Besides Value, you can also use XmlAttribute.InnerText or XmlAttribute.InnerXml to access the text of an attribute. Here is an example of accessing the text of attributes:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Metro System - Stations</title>
</head>
<body>
<h3>Metro System - Stations</h3>
<%
Dim i As Integer
Dim xaStation As XmlAttribute
Dim xnlStations As XmlNodeList
Dim xdStations As New XmlDocument()
Dim strMetroFile = Server.MapPath("App_Data/stations.xml")
If File.Exists(strMetroFile) Then
Using fsStations As New FileStream(strMetroFile, FileMode.Open, FileAccess.Read)
xdStations.Load(fsStations)
xnlStations = xdStations.GetElementsByTagName("station")
For i = 0 To xnlStations.Count - 1
For Each xaStation In xnlStations(i).Attributes
Response.Write("<br>" & xaStation.InnerText)
Next
Next
End Using
End If
%>
</body>
</html>
Getting a Reference to an Attribute
Getting an Attribute as a Node
Many operations require that you get a reference to an attribute before proceeding. To assist you with this, the XmlElement class has a method named GetAttributeNode. Its syntax is:
Public Overridable Function GetAttributeNode(ByVal name As String) As XmlAttribute
Consider the following AutoParts.xml file:
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part item-number="937418">
<year>2012</year>
<make>Toyota</make>
<model trim="LE" engine="1.8L L4" body-style="4-Speed Automatic Transaxle U341E">Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price status="New">58.85</unit-price>
</auto-part>
<auto-part item-number="280486">
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price status="Refurbished">44.45</unit-price>
</auto-part>
<auto-part item-number="580686">
<year>2012</year>
<make>Toyota</make>
<model trim="SE" engine="2.0L L4 Gas" body-style="6-Speed Automatic Transaxle 6F">Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price status="New">14.15</unit-price>
</auto-part>
</auto-parts>
Here is an example of calling this method:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<script runat="server">
</script>
<title>College Park Auto Parts</title>
</head>
<body>
<h3>College Park Auto Parts</h3>
<%
Dim xaBusiness As XmlAttribute
Dim xdAutoParts As new XmlDocument()
Dim strFileName = Server.MapPath("auto-parts.xml")
If File.Exists(strFileName) Then
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
xaBusiness = xdAutoParts.DocumentElement.GetAttributeNode("business")
Response.Write("<br>Attribute Name = " & xaBusiness.Name)
Response.Write("<br>Value = " & xaBusiness.Value)
End Using
End If
%>
</body>
</html>
This would producce:
Getting an Attribute from an Element
Remember that the attributes of an element are stored in a collection. You can use that collection to locate a node, access its attributes, and then get a reference to the desired attribute. Here is an example:
Consider the following XML file named TimeZones.xml:
TimeZones.xml
<?xml version="1.0" encoding="utf-8" ?>
<time-zones>
<zone>
<name initials="CST">Central Standard Time</name>
<utc>-06:00</utc>
<states-and-territories>
<state inclusion="Split" cb-region="East South Central" bea-region="Southeast">Alabama</state>
<state inclusion="Entirely" cb-region="West South Central" bea-region="Southeast">Arkansas</state>
<state inclusion="Split" cb-region="South Atlantic" bea-region="Southeast">Florida</state>
<state inclusion="Entirely" cb-region="West North Central" bea-region="Plains">Minnesota</state>
<state inclusion="Entirely" cb-region="East North Central" bea-region="Great Lakes">Ohio</state>
</states-and-territories>
</zone>
<zone>
<name initials="EST">Eastern Standard Time</name>
<utc>-05:00</utc>
<states-and-territories>
<state inclusion="Split" cb-region="East South Central" bea-region="Southeast">Alabama</state>
<state inclusion="Entirely" cb-region="New England" bea-region="New England">Maine</state>
<state inclusion="Entirely" cb-region="New England" bea-region="New England">Vermont</state>
<state inclusion="Split" cb-region="South Atlantic" bea-region="Southeast">Florida</state>
</states-and-territories>
</zone>
</time-zones>
timezones.aspx
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Time Zones</title>
</head>
<body>
<h3>Time Zones</h3>
<%
Dim xnTimeZone As XmlNode
Dim xaCharacteristic As XmlAttribute
Dim xdTimeZones As New XmlDocument()
Dim xnlTimeZones, xnlStates As XmlNodeList
Dim strFileName = Server.MapPath("exercises/TimeZones.xml")
If File.Exists(strFileName) Then
Using fsTimeZones As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdTimeZones.Load(fsTimeZones)
' Get a list of elements whose names are "name"
xnlTimeZones = xdTimeZones.GetElementsByTagName("name")
' Visit each time zone element
For Each xnTimeZone In xnlTimeZones
' Look for a time zone named Eastern Standard Time
If xnTimeZone.InnerText = "Eastern Standard Time" Then
' Get a list of the third siblings of that node. This represents the states
xnlStates = xnTimeZone.NextSibling.NextSibling.ChildNodes
' Visit each state
For Each xnState In xnlStates
' Look for a state named Florida
If xnState.InnerText = "Florida" Then
' Get its attributes
For Each xaCharacteristic In xnState.Attributes
Response.Write("<br>Attribute: Name = " & xaCharacteristic.Name)
Response.Write("<br>Value: " & xaCharacteristic.Value)
Next
End If
Next
End If
Next
End Using
End If
%>
</body>
</html>
This would produce:
Operations on an XML Attribute
Checking Whether an Element Has Attributes
To let you find out whether an element has at least one attribute, the XmlElement class is equipped with a method named HasAttributes. Its syntax is:
Public Overridable ReadOnly Property HasAttributes As Boolean
Consider the following XML file: roads.xml:
<?xml version="1.0" encoding="utf-8" ?>
<roads>
<road>
<road-name length-rank="1">I-90</road-name>
<road-type>Interstate</road-type>
<distance km="4861.09">3020.54</distance>
<location>From the Edgar Martinez Drv South to Boston, MA</location>
<intersections>
<intersection>
<intersecting>SR 519</intersecting>
<in-near>Seattle, WA</in-near>
</intersection>
<intersection>
<intersecting>I-5</intersecting>
<in-near>Seattle, WA</in-near>
</intersection>
</intersections>
</road>
<road>
<road-name length-rank="4">I-10</road-name>
<road-type>Interstate</road-type>
<distance km="3959.53">2460.34</distance>
<location>From SR-1 (California State Route 1) to I-95 in Jacksonville, FL</location>
<intersections>
<intersection>
<intersecting>SR 1</intersecting>
<in-near>Santa Monica, CA</in-near>
</intersection>
<intersection>
<intersecting>I-5</intersecting>
<in-near>Los Angeles, CA</in-near>
</intersection>
</intersections>
</road>
</roads>
Here is an example:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Road System Database</title>
</head>
<body>
<h3>Road System Database</h3>
<%
Dim xnRoad As XmlNode
Dim xnlRoads As XmlNodeList
Dim strFileName = Server.MapPath("App_Data/roads.xml")
Dim xdRoads As New XmlDocument()
If File.Exists(strFileName) Then
Using fsRoads = New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdRoads.Load(fsRoads)
' Get a list of elements whose names are "road-name"
xnlRoads = xdRoads.GetElementsByTagName("road-name")
' Visit each road element
For Each xnRoad In xnlRoads
' Look for a road named I-10
If xnRoad.InnerText = "I-10" Then
If CType(xnRoad, XmlElement).HasAttributes = True Then
Response.Write("<br>Road " & xnRoad.InnerText & " has at least one attribute.")
Else
Response.Write("<br>Road " & xnRoad.InnerText & " ain't got no attribute(s).")
End If
End If
If CType(xnRoad.NextSibling, XmlElement).HasAttributes = True Then
Response.Write("<br>Road Type " & xnRoad.NextSibling.InnerText & " has at least one attribute.")
Else
Response.Write("<br>Road Type " & xnRoad.NextSibling.InnerText & " ain't got no attribute(s).")
End If
Next
End Using
End If
%>
</body>
</html>
Here is an example of running the program:
Adding an Attribute to an Element
An element can have 0, one, or more attributes. The attributes of an element are stored in the Attributes property of an XmlElement object. The XmlElement.Attributes property is based on a class called XmlAttributeCollection. The XmlAttributeCollection class is based on the XmlNamedNodeMap class.
Before performing an attribute-related operation on an element, to find out whether the element has any attribute, you can check the value of the Boolean HasAttributes property of its XmlElement element. If this property produces a true value, then the element has at least one attribute; otherwise, the element doesn't have any.
While a certain element may have an attribute, a sibling element with the same name may not have an attribute or may have a completely different type of attribute. Here is an XML file with attributes in some elements:
<?xml version="1.0" encoding="utf-8" ?>
<videos>
<video ISBN="0-7888-1623-3">
<title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
<director>Jonathan Lynn</director>
<length>112 Minutes</length>
<format>DVD</format>
<rating>R</rating>
</video>
<video>
<title WrittenBy="Charlie Peter">Her Alibi</title>
<director>Bruce Beresford</director>
<length>94 Mins</length>
<format>DVD</format>
<rating>PG-13</rating>
</video>
</videos>
Remember that you can include white spaces to make your code easy to read. This means that you can type an attribute on the next line of its element's name. We know that every element must be closed. We saw that we could close an element with an end-tag as follows:
<video><ISBN>0-7888-1623-3</ISBN></video>
We also saw that we could close an element locally as follows: <video />. If you create an attribute in an empty element, you can also close it by typing the indicative forward slash before the right angle bracket and after an empty space. Here is an example:
<video ISBN="0-7888-1623-3" />
Setting an Attribute by Name and Value
As mentioned already, an attribute primarily belongs to an element. This means that, when creating an attribute, you must specify what element it would belong to. To support the attributes of an element, the XmlElement class is equipped with the SetAttribute() method which is overloaded in two versions. The first version of this method uses the following syntax:
Public Overridable Sub SetAttribute(ByVal name As String, ByVal value As String)
The first argument is the name of the new attribute and the second argument will be its text. Before adding an attribute, you should first identify its parent element. Consider the following file named AutoParts.xml:
<?xml version="1.0" encoding="UTF-8"?>
<auto-parts>
<auto-part>
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price>58.85</unit-price>
</auto-part>
<auto-part>
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price>44.45</unit-price>
</auto-part>
<auto-part>
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price>14.15</unit-price>
</auto-part>
</auto-parts>
Here is an example that adds an attribute to the root element:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>College Park Auto Parts</title>
</head>
<body>
<h3>College Park Auto Parts</h3>
<%
Dim xdAutoParts As New XmlDocument()
Dim strFileName = Server.MapPath("auto-parts.xml")
If File.Exists(strFileName) Then
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
End Using
Using fsAutoParts As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
' Create an attribute and add it to the root element
xdAutoParts.DocumentElement.SetAttribute("business", "College Park Auto-Parts")
' Save the file
xdAutoParts.Save(fsAutoParts)
End Using
End If
%>
</body>
</html>
From the above file, this code would result in:
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part>
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price>58.85</unit-price>
</auto-part>
<auto-part>
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price>44.45</unit-price>
</auto-part>
<auto-part>
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price>14.15</unit-price>
</auto-part>
</auto-parts>
Programmatically Creating an Attribute
To support attribute addition, the XmlDocument class is equipped with the CreateAttribute() method, which is overloaded in three versions. The first version of this method has the following syntax:
Public Function CreateAttribute(ByVal name As String) As XmlAttribute
This method expects the name of the attribute as argument. If it succeeds, this method produces an XmlAttribute object.
Adding Many Attributes to an Element
To let you add a new attribute to an element, the XmlElement class is equipped with a method named SetAttributeNote. This method is overloaded with two versions. One of the versions uses the following syntax:
Public Overridable Function SetAttributeNode(ByVal newAttr As XmlAttribute) As XmlAttribute
This method expects an XmlAttribute object. Here is an example that looks for a particular node in a collection and adds an attribute to it:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>College Park Auto Parts</title>
</head>
<body>
<h3>College Park Auto Parts</h3>
<%
Dim i As Integer
Dim xnlYears As XmlNodeList
Dim xaItemNumber As XmlAttribute
Dim xdAutoParts As New XmlDocument()
Dim strFileName = Server.MapPath("auto-parts1.xml")
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
End Using
Using fsAutoParts As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
' Create an attribute
xaItemNumber = xdAutoParts.CreateAttribute("item-number")
xaItemNumber.Value = "280486"
' Get a list of elements whose names are "year"
xnlYears = xdAutoParts.GetElementsByTagName("year")
' Visit each auto part element
For i = 0 To xnlYears.Count - 1
' Look for an auto part that has the year 2015
If xnlYears(i).InnerText = "2015" Then
' Once you find that auto-part, add the new attribute to it
CType(xnlYears(i).ParentNode, XmlElement).SetAttributeNode(xaItemNumber)
' Save the file
xdAutoParts.Save(fsAutoParts)
End If
Next
End Using
%>
</body>
</html>
From the above file, this code would result in:
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part>
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price>58.85</unit-price>
</auto-part>
<auto-part item-number="280486">
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price>44.45</unit-price>
</auto-part>
<auto-part>
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price>14.15</unit-price>
</auto-part>
</auto-parts>
You might have noticed that the above code made a comparison on the value of only one element, and that type of value (of the year element) is used by more than one element (year = 2012). If you perform the same comparison on a value that is repeated, you would receive an error. Consider the following example:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>College Park Auto Parts</title>
</head>
<body>
<h3>College Park Auto Parts</h3>
<%
Dim i As Integer
Dim xnlYears As XmlNodeList
Dim xaItemNumber As XmlAttribute
Dim xdAutoParts As New XmlDocument()
Dim strFileName = Server.MapPath("App_Data/auto-parts.xml")
If File.Exists(strFileName) Then
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
End Using
Using fsAutoParts As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
' Create an attribute
xaItemNumber = xdAutoParts.CreateAttribute("item-number")
xaItemNumber.Value = "580686"
' Get a list of elements whose names are "year"
xnlYears = xdAutoParts.GetElementsByTagName("year")
' Visit each auto part element
For i = 0 To xnlYears.Count - 1
' Look for an auto part that has the year 2015
If (xnlYears(i).InnerText = "2012") Then
' Once you find that auto-part, add the new attribute to it
CType(xnlYears(i).ParentNode, XmlElement).SetAttributeNode(xaItemNumber)
End If
Next
' Save the file
xdAutoParts.Save(fsAutoParts)
End Using
End If
%>
</body>
</html>
This code would produce an error. An unprofessional solution is to perform the comparison on all or other values of the same element. Here is an example:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>College Park Auto Parts</title>
</head>
<body>
<h3>College Park Auto Parts</h3>
<%
Dim i As Integer
Dim xnlYears As XmlNodeList
Dim xaItemNumber As XmlAttribute
Dim xdAutoParts As New XmlDocument()
Dim strFileName = Server.MapPath("App_Data/auto-parts.xml")
If File.Exists(strFileName) Then
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
End Using
Using fsAutoParts As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
' Create an attribute
xaItemNumber = xdAutoParts.CreateAttribute("item-number")
xaItemNumber.Value = "580686"
' Get a list of elements whose names are "year"
xnlYears = xdAutoParts.GetElementsByTagName("year")
' Visit each auto part element
For i = 0 To xnlYears.Count - 1
' Look for an auto part that has the year 2015
If (xnlYears(i).InnerText = "2012") And
(xnlYears(i).NextSibling.InnerText = "Toyota") And
(xnlYears(i).NextSibling.NextSibling.InnerText = "Corolla") And
(xnlYears(i).NextSibling.NextSibling.NextSibling.InnerText = "Air Filters") And
(xnlYears(i).NextSibling.NextSibling.NextSibling.NextSibling.InnerText = "FRAM CF10285 Fresh Breeze Cabin Air Filter") Then
' Once you find that auto-part, add the new attribute to it
CType(xnlYears(i).ParentNode, XmlElement).SetAttributeNode(xaItemNumber)
End If
Next
' Save the file
xdAutoParts.Save(fsAutoParts)
End Using
End If
%>
</body>
</html>
This would produce:
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part>
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price>58.85</unit-price>
</auto-part>
<auto-part item-number="280486">
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price>44.45</unit-price>
</auto-part>
<auto-part item-number="580686">
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price>14.15</unit-price>
</auto-part>
</auto-parts>
We referred to this solution as "unprofessional" because there is no guaranty that two elements cannot have the exact same characteristics (same car make, same model, same year, same part name). The better solution used in databases is to give a unique characteristic, sometimes called a unique key, to each record. For our auto-parts application, this would correspond to giving a unique item number to each auto part.
By using the collection of attributes of an element, you can locate an attribute in an element and take an appropriate action, such as adding an attribute to a sibling of the element. Here is an example:
College Park Auto-Parts: auto-parts.xml
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part item-number="937418">
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price>58.85</unit-price>
</auto-part>
<auto-part item-number="280486">
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price>44.45</unit-price>
</auto-part>
<auto-part item-number="580686">
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price>14.15</unit-price>
</auto-part>
</auto-parts>
College Park Auto-Parts: auto-parts.apx
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>College Park Auto Parts</title>
</head>
<body>
<h3>College Park Auto Parts</h3>
<%
Dim i As Integer
Dim xaTrim As XmlAttribute
Dim xdAutoParts As New XmlDocument()
Dim strFileName = Server.MapPath("App_Data/auto-parts.xml")
If File.Exists(strFileName) Then
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
End Using
Dim xnlAutoParts As XmlNodeList = xdAutoParts.GetElementsByTagName("auto-part")
For i = 0 To xnlAutoParts.Count - 1
For Each xaPart In xnlAutoParts(i).Attributes
If (xaPart.Name = "item-number") And (xaPart.Value = "937418") Then
' Create an attribute
xaTrim = xdAutoParts.CreateAttribute("trim")
xaTrim.Value = "LE"
CType(xnlAutoParts(i).FirstChild.NextSibling.NextSibling, XmlElement).SetAttributeNode(xaTrim)
Using fsAutoParts As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
xdAutoParts.Save(fsAutoParts)
End Using
End If
Next
Next
End If
%>
</body>
</html>
This would produce:
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part item-number="937418">
<year>2012</year>
<make>Toyota</make>
<model trim="LE">Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price>58.85</unit-price>
</auto-part>
<auto-part item-number="280486">
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price>44.45</unit-price>
</auto-part>
<auto-part item-number="580686">
<year>2012</year>
<make>Toyota</make>
<model>Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price>14.15</unit-price>
</auto-part>
</auto-parts>
Adding Many Attributes
In the same, you can create as many attributes as you want. Here are examples:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>College Park Auto Parts</title>
</head>
<body>
<h3>College Park Auto Parts</h3>
<%
Dim i As Integer
Dim xaNewPart As XmlAttribute
Dim xdAutoParts As New XmlDocument()
Dim strFileName = Server.MapPath("App_Data/auto-parts.xml")
If File.Exists(strFileName) Then
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
End Using
Dim xnlAutoParts As XmlNodeList = xdAutoParts.GetElementsByTagName("auto-part")
For i = 0 To xnlAutoParts.Count - 1
For Each xaPart In xnlAutoParts(i).Attributes
' New Attribute
xaNewPart = xdAutoParts.CreateAttribute("status")
xaNewPart.Value = "New"
CType(xnlAutoParts(i).FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling, XmlElement).SetAttributeNode(xaNewPart)
If (xaPart.Name = "item-number") And (xaPart.Value = "937418") Then
' New Attribute
xaNewPart = xdAutoParts.CreateAttribute("engine")
xaNewPart.Value = "1.8L L4"
CType(xnlAutoParts(i).FirstChild.NextSibling.NextSibling, XmlElement).SetAttributeNode(xaNewPart)
' New Attribute
xaNewPart = xdAutoParts.CreateAttribute("body-style")
xaNewPart.Value = "4-Speed Automatic Transaxle U341E"
CType(xnlAutoParts(i).FirstChild.NextSibling.NextSibling, XmlElement).SetAttributeNode(xaNewPart)
End If
If (xaPart.Name = "item-number") And (xaPart.Value = "580686") Then
' New Attribute
xaNewPart = xdAutoParts.CreateAttribute("trim")
xaNewPart.Value = "SE"
CType(xnlAutoParts(i).FirstChild.NextSibling.NextSibling, XmlElement).SetAttributeNode(xaNewPart)
' New Attribute
xaNewPart = xdAutoParts.CreateAttribute("engine")
xaNewPart.Value = "2.0L L4 Gas"
CType(xnlAutoParts(i).FirstChild.NextSibling.NextSibling, XmlElement).SetAttributeNode(xaNewPart)
' New Attribute
xaNewPart = xdAutoParts.CreateAttribute("body-style")
xaNewPart.Value = "6-Speed Automatic Transaxle 6F"
CType(xnlAutoParts(i).FirstChild.NextSibling.NextSibling, XmlElement).SetAttributeNode(xaNewPart)
End If
Using fsAutoParts As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
xdAutoParts.Save(fsAutoParts)
End Using
Next
Next
End If
%>
</body>
</html>
This would produce:
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part item-number="937418">
<year>2012</year>
<make>Toyota</make>
<model trim="LE" engine="1.8L L4" body-style="4-Speed Automatic Transaxle U341E">Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price status="New">58.85</unit-price>
</auto-part>
<auto-part item-number="280486">
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price status="New">44.45</unit-price>
</auto-part>
<auto-part item-number="580686">
<year>2012</year>
<make>Toyota</make>
<model trim="SE" engine="2.0L L4 Gas" body-style="6-Speed Automatic Transaxle 6F">Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price status="New">14.15</unit-price>
</auto-part>
</auto-parts>
Appending an Attribute
Appending an attribute consists of adding an attribute to an element. Imagine the element already has at least one attribute:
<?xml version="1.0" encoding="utf-8"?>
<periodic-table>
<element>
<atomic-number>1</atomic-number>
<name>Hydrogen</name>
<symbol>H</symbol>
<atomic-mass>1.0079</atomic-mass>
</element>
<element>
<atomic-number column="18">2</atomic-number>
<name>Helium</name>
<symbol>He</symbol>
<atomic-mass>4.002682</atomic-mass>
</element>
</periodic-table>
In this case, the new one is positioned to the end of the collection of the attributes of the element. To support this operation, the XmlAttributeCollection class is equipped with a method named Append. Its syntax is:
Public Function Append(ByVal node As XmlAttribute) As XmlAttribute
Here is an example:
chemistry.xml:
<?xml version="1.0" encoding="utf-8"?>
<periodic-table>
<element>
<atomic-number>1</atomic-number>
<name>Hydrogen</name>
<symbol>H</symbol>
<atomic-mass>1.0079</atomic-mass>
</element>
<element>
<atomic-number column="18">2</atomic-number>
<name>Helium</name>
<symbol>He</symbol>
<atomic-mass>4.002682</atomic-mass>
</element>
</periodic-table>
chemistry.aspx:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Chemistry - Periodic Table</title>
</head>
<body>
<h3>Chemistry - Periodic Table</h3>
<%
Dim xaElement As XmlAttribute
Dim xnlElements As XmlNodeList
Dim strFileName = Server.MapPath("App_Data/chemistry.xml")
Dim xdPeriodicTable As XmlDocument = New XmlDocument()
If File.Exists(strFileName) Then
Using fsPeriodicTable As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdPeriodicTable.Load(fsPeriodicTable)
End Using
' New Attribute
xaElement = xdPeriodicTable.CreateAttribute("row")
xaElement.Value = "1"
xnlElements = xdPeriodicTable.GetElementsByTagName("atomic-number")
For Each xnElement In xnlElements
If xnElement.InnerText = "2" Then
xnElement.Attributes.Append(xaElement)
Using fsPeriodicTable As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
' Save the file
xdPeriodicTable.Save(fsPeriodicTable)
End Using
End If
Next
End If
%>
</body>
</html>
This would produce:
<?xml version="1.0" encoding="utf-8"?>
<periodic-table>
<element>
<atomic-number>1</atomic-number>
<name>Hydrogen</name>
<symbol>H</symbol>
<atomic-mass>1.0079</atomic-mass>
</element>
<element>
<atomic-number column="18" row="1">2</atomic-number>
<name>Helium</name>
<symbol>He</symbol>
<atomic-mass>4.002682</atomic-mass>
</element>
</periodic-table>
If the element doesn't have any attribute(s), the new one is created as the only one.
Prepending an Attribute
Prepending an attribute consists of adding a new attribute to an element. If the element doesn't have any attribute yet, the new attribute is created as the only one. If the element already has at least one attribute, the new one is positioned at the beginning of the collection. To support this operation, the XmlAttributeCollection class is equipped with a method named Prepend. Its syntax is:
Public Function Prepend(ByVal node As XmlAttribute) As XmlAttribute
Here is an example:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Chemistry - Periodic Table</title>
</head>
<body>
<h3>Chemistry - Periodic Table</h3>
<%
Dim xnElement As XmlNode
Dim xaElement As XmlAttribute
Dim xnlElements As XmlNodeList
Dim xdPeriodicTable As XmlDocument = New XmlDocument()
Dim strFileName = Server.MapPath("App_Data/chemistry.xml")
If File.Exists(strFileName) Then
Using fsPeriodicTable = New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdPeriodicTable.Load(fsPeriodicTable)
End Using
' New Attribute
xaElement = xdPeriodicTable.CreateAttribute("column")
xaElement.Value = "1"
xnlElements = xdPeriodicTable.GetElementsByTagName("atomic-number")
For Each xnElement In xnlElements
If xnElement.InnerText = "1" Then
xnElement.Attributes.Prepend(xaElement)
End If
Next
Using fsPeriodicTable As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
xdPeriodicTable.Save(fsPeriodicTable)
End Using
End If
%>
</body>
</html>
This would produce:
<?xml version="1.0" encoding="utf-8"?>
<periodic-table>
<element>
<atomic-number column="1" row="1">1</atomic-number>
<name>Hydrogen</name>
<symbol>H</symbol>
<atomic-mass>1.0079</atomic-mass>
</element>
<element>
<atomic-number column="18" row="1">2</atomic-number>
<name>Helium</name>
<symbol>He</symbol>
<atomic-mass>4.002682</atomic-mass>
</element>
</periodic-table>
Inserting an Attribute
To create a new attribute before it, you can call the XmlAttributeCollection.InsertBefore() method. Its syntax is:
Public Function InsertBefore(ByVal newNode As XmlAttribute, ByVal refNode As XmlAttribute) As XmlAttribute
To add a new attribute after the current one, you can call the XmlAttributeCollection.InsertAfter() method. Its syntax is:
Public Function InsertAfter(ByVal newNode As XmlAttribute, ByVal refNode As XmlAttribute) As XmlAttribute
The Parent of an Attribute
Once an attribute has been created, to identify the element to which it belongs, you can access its XmlAttribute.OwnerElement property. This property produces an XmlElement value:
Public Overridable ReadOnly Property OwnerElement As XmlElement
Editing/Updating an Attribute
Editing or updating an attribute consists of changing something about it, such as its value. You have many options.
To edit or update an attribute, you can start by locating it. This time too, you have many options. The classic way is to use a series of loops to navige both the elements and their attributes to locate the particular attribute you want. Here is an example:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>College Park Auto-Parts - Part Update</title>
</head>
<body>
<h3>College Park Auto-Parts - Part Update</h3>
<%
Dim i As Integer
Dim xdAutoParts As New XmlDocument()
Dim xnlAutoParts, xnlUnitPrices As XmlNodeList
Dim strFileName = Server.MapPath("App_Data/auto-parts.xml")
If File.Exists(strFileName) Then
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
End Using
xnlAutoParts = xdAutoParts.GetElementsByTagName("auto-part")
For i = 0 To xnlAutoParts.Count - 1
For Each xaPart In xnlAutoParts(i).Attributes
If (xaPart.Name = "item-number") And (xaPart.Value = "280486") Then
xnlUnitPrices = xnlAutoParts(i).ChildNodes
For Each xnUnitPrice In xnlUnitPrices
If xnUnitPrice.Name = "unit-price" Then
For Each xaStatus In xnUnitPrice.Attributes
If xaStatus.Name = "status" Then
. . .
End If
Next
End If
Next
End If
Next
Next
End If
%>
</body>
</html>
After accessing the attribute, you can manipulate it as you see fit. For example, you can change its value. Here is an example:
College Park Auto-Parts: auto-parts.xml
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part item-number="937418">
<year>2012</year>
<make>Toyota</make>
<model trim="LE" engine="1.8L L4" body-style="4-Speed Automatic Transaxle U341E">Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price status="New">58.85</unit-price>
</auto-part>
<auto-part item-number="280486">
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-pricestatus="New">44.45</unit-price>
</auto-part>
<auto-part item-number="580686">
<year>2012</year>
<make>Toyota</make>
<model trim="SE" engine="2.0L L4 Gas" body-style="6-Speed Automatic Transaxle 6F">Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price status="New">14.15</unit-price>
</auto-part>
</auto-parts>
College Park Auto-Parts: edit-part.aspx
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>College Park Auto-Parts - Part Update</title>
</head>
<body>
<h3>College Park Auto-Parts - Part Update</h3>
<%
Dim i As Integer
Dim xdAutoParts As New XmlDocument()
Dim xnlAutoParts, xnlUnitPrices As XmlNodeList
Dim strFileName = Server.MapPath("App_Data/auto-parts.xml")
If File.Exists(strFileName) Then
Using fsAutoParts As New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdAutoParts.Load(fsAutoParts)
End Using
xnlAutoParts = xdAutoParts.GetElementsByTagName("auto-part")
For i = 0 To xnlAutoParts.Count - 1
For Each xaPart In xnlAutoParts(i).Attributes
If (xaPart.Name = "item-number") And (xaPart.Value = "280486") Then
xnlUnitPrices = xnlAutoParts(i).ChildNodes
For Each xnUnitPrice In xnlUnitPrices
If xnUnitPrice.Name = "unit-price" Then
For Each xaStatus In xnUnitPrice.Attributes
If xaStatus.Name = "status" Then
xaStatus.InnerText = "Refurbished"
End If
Next
End If
Next
End If
Next
Next
Using fsAutoParts As New FileStream(strFileName, FileMode.Create, FileAccess.Write)
xdAutoParts.Save(fsAutoParts)
End Using
End If
%>
</body>
</html>
This would produce:
<?xml version="1.0" encoding="utf-8"?>
<auto-parts business="College Park Auto-Parts">
<auto-part item-number="937418">
<year>2012</year>
<make>Toyota</make>
<model trim="LE" engine="1.8L L4" body-style="4-Speed Automatic Transaxle U341E">Corolla</model>
<category>Shocks, Struts & Suspension</category>
<part-name>KYB SM5215 Strut mount</part-name>
<unit-price status="New">58.85</unit-price>
</auto-part>
<auto-part item-number="280486">
<year>2015</year>
<make>Ford</make>
<model>Escape</model>
<category>Brake System</category>
<part-name>Power Stop (16-1044) Z16 Ceramic Brake Pad</part-name>
<unit-price status="Refurbished">44.45</unit-price>
</auto-part>
<auto-part item-number="580686">
<year>2012</year>
<make>Toyota</make>
<model trim="SE" engine="2.0L L4 Gas" body-style="6-Speed Automatic Transaxle 6F">Corolla</model>
<category>Air Filters</category>
<part-name>FRAM CF10285 Fresh Breeze Cabin Air Filter</part-name>
<unit-price status="New">14.15</unit-price>
</auto-part>
</auto-parts>
Removing Attributes
Deleting an Attribute by its Name
If an element has an attribute you don't want or that you don't need anymore, you can delete that attribute. You have various options, two are available through the XmlElement class.
Using the XmlElement.RemoveAttributeAt() method to delete an attribute can be uncertain because you would not know whether there is an attribute at the specified position. An alternative is to specify the name of the attribute you want to delete. To support this, the XmlElement class is equipped with the RemoveAttribute() method, which is overloaded with two versions. One of the versions of this method uses the following syntax:
Public Overridable Sub RemoveAttribute(ByVal name As String)
This method expects as argument the name of the attribute to remove. Consider the following file named TimeZones.xml:
<?xml version="1.0" encoding="utf-8" ?>
<time-zones>
<zone>
<name initials="CST">Central Standard Time</name>
<utc>-06:00</utc>
<states-and-territories>
<state inclusion="Split" cb-region="East South Central" bea-region="Southeast">Alabama</state>
<state inclusion="Entirely" cb-region="West South Central" bea-region="Southeast">Arkansas</state>
<state inclusion="Split" cb-region="South Atlantic" bea-region="Southeast">Florida</state>
<state inclusion="Entirely" cb-region="West North Central" bea-region="Plains">Minnesota</state>
<state inclusion="Entirely" cb-region="East North Central" bea-region="Great Lakes">Ohio</state>
</states-and-territories>
</zone>
<zone>
<name initials="EST">Eastern Standard Time</name>
<utc>-05:00</utc>
<states-and-territories>
<state inclusion="Split" cb-region="East South Central" bea-region="Southeast">Alabama</state>
<state inclusion="Entirely" cb-region="New England" bea-region="New England">Maine</state>
<state inclusion="Entirely" cb-region="New England" bea-region="New England">Vermont</state>
<state inclusion="Split" cb-region="South Atlantic" bea-region="Southeast">Florida</state>
</states-and-territories>
</zone>
</time-zones>
Here is an example of calling this method:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Chemistry - Periodic Table</title>
</head>
<body>
<h3>Chemistry - Periodic Table</h3>
<%
Dim xnTimeZone As XmlNode
Dim xnlTimeZones, xnlStates As XmlNodeList
Dim xdTimeZones As XmlDocument = New XmlDocument()
Dim strFileName = Server.MapPath("App_Data/TimeZones.xml")
If File.Exists(strFileName) Then
Using fsTimeZones = New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdTimeZones.Load(fsTimeZones)
End Using
' Get a list of elements whose names are "name"
xnlTimeZones = xdTimeZones.GetElementsByTagName("name")
Try
' Visit each time zone element
For Each xnTimeZone In xnlTimeZones
' Look for a time zone named Eastern Standard Time
If xnTimeZone.InnerText = "Eastern Standard Time" Then
' Get a list of the third siblings of that node. This represents the states
xnlStates = xnTimeZone.NextSibling.NextSibling.ChildNodes
' Visit each state
For Each xnState In xnlStates
' Look for a state named Florida
If xnState.InnerText = "Florida" Then
' Get its attributes
For Each xaCharacteristics In xnState.Attributes
If xaCharacteristics.Name = "cb-region" Then
CType(xnState, XmlElement).RemoveAttribute("cb-region")
Using fsTimeZones = New FileStream(strFileName, FileMode.Create, FileAccess.Write)
xdTimeZones.Save(fsTimeZones)
End Using
End If
Next
End If
Next
End If
Next
Catch ioe As InvalidOperationException
End Try
End If
%>
</body>
</html>
This would produce:
<?xml version="1.0" encoding="utf-8"?>
<time-zones>
<zone>
<name initials="CST">Central Standard Time</name>
<utc>-06:00</utc>
<states-and-territories>
<state inclusion="Split" cb-region="East South Central" bea-region="Southeast">Alabama</state>
<state inclusion="Entirely" cb-region="West South Central" bea-region="Southeast">Arkansas</state>
<state inclusion="Split" cb-region="South Atlantic" bea-region="Southeast">Florida</state>
<state inclusion="Entirely" cb-region="West North Central" bea-region="Plains">Minnesota</state>
<state inclusion="Entirely" cb-region="East North Central" bea-region="Great Lakes">Ohio</state>
</states-and-territories>
</zone>
<zone>
<name initials="EST">Eastern Standard Time</name>
<utc>-05:00</utc>
<states-and-territories>
<state inclusion="Split" cb-region="East South Central" bea-region="Southeast">Alabama</state>
<state inclusion="Entirely" cb-region="New England" bea-region="New England">Maine</state>
<state inclusion="Entirely" cb-region="New England" bea-region="New England">Vermont</state>
<state inclusion="Split" bea-region="Southeast">Florida</state>
</states-and-territories>
</zone>
</time-zones>
Removing an Attribute by Position
The attributes of an XmlElement object are considered stored in an indexed list with the most left attribute at index 0, the second from left at index 1, and so on. Based on this, to remove an attribute by locating it based on its index, you can call the XmlElement.RemoveAttributeAt() method. Its syntax is:
Public Overridable Function RemoveAttributeAt(ByVal i As Integer) As XmlNode
When calling this method, if an attribute exists at position i, it will be deleted and the method would return it. If there is no attribute at that index, the method doesn't do anything and it returns 0.
Using the list of attributes of an element, you can delete one or all attributes of an element. Since the attributes are stored in a collection, you can locate the undesired attribute by its index and then delete it. To do this, you can call the XmlAttributeCollection.RemoveAt() method. Its syntax is:
Public Function RemoveAt(ByVal i As Integer) As XmlAttribute
This method expects the index of the attribute that needs to be removed. As mentioned for the XmlAttributeCollection.ItemOf indexed property, to efficiently use this RemoveAt() method, you should know the exact index of the attribute, otherwise, you may access and therefore delete the wrong attribute. Here is an example:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Time Zones</title>
</head>
<body>
<h3>Time Zones</h3>
<%
Dim i As Integer
Dim xnTimeZone, xnState As XmlNode
Dim xnlTimeZones, xnlStates As XmlNodeList
Dim xdTimeZones As XmlDocument = New XmlDocument()
Dim strFileName = Server.MapPath("App_Data/TimeZones.xml")
If File.Exists(strFileName) Then
Using fsTimeZones = New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdTimeZones.Load(fsTimeZones)
End Using
' Get a list of elements whose names are "name"
xnlTimeZones = xdTimeZones.GetElementsByTagName("name")
Try
' Visit each time zone element
For Each xnTimeZone In xnlTimeZones
' Look for a time zone named Eastern Standard Time
If xnTimeZone.InnerText = "Eastern Standard Time" Then
' Get a list of the third siblings of that node. This represents the states
xnlStates = xnTimeZone.NextSibling.NextSibling.ChildNodes
' Visit each state
For Each xnState In xnlStates
' Look for a state named Maine
If xnState.InnerText = "Maine" Then
' Get its attributes
For i = 0 To xnState.Attributes.Count - 1
If xnState.Attributes(i).Name = "bea-region" Then
CType(xnState, XmlElement).RemoveAttributeAt(i)
Using fsTimeZones = New FileStream(strFileName, FileMode.Create, FileAccess.Write)
xdTimeZones.Save(fsTimeZones)
End Using
End If
Next
End If
Next
End If
Next
Catch ioe As InvalidOperationException
End Try
End If
%>
</body>
</html>
Removing an Attribute Based on its Name
Another technique you can use consists of defining an XmlAttribute object and submitting to its XmlElement parent to delete. To do this, you can call the RemoveAttributeNode() method of the XmlElement object. Its syntax is:
Public Overridable Function RemoveAttributeNode(ByVal oldAttr As XmlAttribute) As XmlAttribute
When calling this method, pass the attribute object as argument. If the attribute exists, it would be removed and the method would return the deleted attribute. If the attribute doesn't exist, nothing would happen. Here is an example:
An alternative is to explicitly identify the attribute you want to delete. To do this, you can call the XmlAttributeCollection.Remove() method. Its syntax is:
Public Function Remove(ByVal node As XmlAttribute) As XmlAttribute
This method takes as attribute the XmlAttribute identification of the attribute you want to remove.
Clearing an Element of Attributes
To delete all attributes of an element, you can call the XmlAttributeCollection.RemoveAll() method. Its syntax is:
Public Sub RemoveAll
This method would simply remove all attributes that belong to an XmlElement object. Here is an example:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="System.Xml" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>Time Zones</title>
</head>
<body>
<h3>Time Zones</h3>
<%
Dim i As Integer
Dim xnTimeZone, xnState As XmlNode
Dim xnlTimeZones, xnlStates As XmlNodeList
Dim xdTimeZones As XmlDocument = New XmlDocument()
Dim strFileName = Server.MapPath("App_Data/TimeZones.xml")
If File.Exists(strFileName) Then
Using fsTimeZones = New FileStream(strFileName, FileMode.Open, FileAccess.Read)
xdTimeZones.Load(fsTimeZones)
End Using
' Get a list of elements whose names are "name"
xnlTimeZones = xdTimeZones.GetElementsByTagName("name")
' Visit each time zone element
For Each xnTimeZone In xnlTimeZones
' Look for a time zone named Eastern Standard Time
If xnTimeZone.InnerText = "Eastern Standard Time" Then
' Get a list of the third siblings of that node. This represents the states
xnlStates = xnTimeZone.NextSibling.NextSibling.ChildNodes
' Visit each state
For Each xnState In xnlStates
' Look for a state named Florida
If xnState.InnerText = "Florida" Then
xnState.Attributes.RemoveAll()
Using fsTimeZones = New FileStream(strFileName, FileMode.Create, FileAccess.Write)
xdTimeZones.Save(fsTimeZones)
End Using
End If
Next
End If
Next
End If
%>
</body>
</html>
This would produce:
<?xml version="1.0" encoding="utf-8"?>
<time-zones>
<zone>
<name initials="CST">Central Standard Time</name>
<utc>-06:00</utc>
<states-and-territories>
<state inclusion="Split" cb-region="East South Central" bea-region="Southeast">Alabama</state>
<state inclusion="Entirely" cb-region="West South Central" bea-region="Southeast">Arkansas</state>
<state inclusion="Split" cb-region="South Atlantic" bea-region="Southeast">Florida</state>
<state inclusion="Entirely" cb-region="West North Central" bea-region="Plains">Minnesota</state>
<state inclusion="Entirely" cb-region="East North Central" bea-region="Great Lakes">Ohio</state>
</states-and-territories>
</zone>
<zone>
<name initials="EST">Eastern Standard Time</name>
<utc>-05:00</utc>
<states-and-territories>
<state inclusion="Split" cb-region="East South Central" bea-region="Southeast">Alabama</state>
<state inclusion="Entirely" cb-region="New England">Maine</state>
<state inclusion="Entirely" cb-region="New England" bea-region="New England">Vermont</state>
<state>Florida</state>
</states-and-territories>
</zone>
</time-zones>