XPath help please

[roidy]

Take the following xml file:-

<Data>
<Fruit>
<Name>Apple</Name>
<Color>Green</Color>
<Value>100</Value>
</Fruit>
<Name>Orange</Name>
<Color>Orange</Color>
<Value>75</Value>
</Fruit>
<Fruit>
<Name>Plum</Name>
<Color>Purple</Color>
</Fruit>
</Data>

Now in code I`m looping through 'Fruit' nodes:-

Dim xpathDoc = New XPathDocument("test.xml")
Dim xmlNav = xpathDoc.CreateNavigator()
Dim xmlNI = xmlNav.Select("/Data/Fruit")

While (xmlNI.MoveNext())

How to get the value of Name node?
How to get the value of Color node?
How to get the value of Value node?

End While


I`ve looked at quite a few examples and none explain how to get the value of
a child node of the current node. Help please.

Rob

 

[roidy]

Ok here`s what I`ve come up with:-

While (xmlNI.MoveNext())

If xmlNI.Current.MoveToChild("Name", "") Then
name = xmlNI.Current.Value
xmlNI.Current.MoveToParent()
End If

If xmlNI.Current.MoveToChild("Color", "") Then
color= xmlNI.Current.Value
xmlNI.Current.MoveToParent()
End If

If xmlNI.Current.MoveToChild("Value", "") Then
value= xmlNI.Current.Value
xmlNI.Current.MoveToParent()
End If

End While


This works but is it the best way to do it?

Rob

 

[Martin Honnen]

Take the following xml file:-

<Data>
<Fruit>
<Name>Apple</Name>
<Color>Green</Color>
<Value>100</Value>
</Fruit>
<Name>Orange</Name>
<Color>Orange</Color>
<Value>75</Value>
</Fruit>
<Fruit>
<Name>Plum</Name>
<Color>Purple</Color>
</Fruit>
</Data>

Now in code I`m looping through 'Fruit' nodes:-

Dim xpathDoc = New XPathDocument("test.xml")
Dim xmlNav = xpathDoc.CreateNavigator()
Dim xmlNI = xmlNav.Select("/Data/Fruit")

While (xmlNI.MoveNext())

How to get the value of Name node?
How to get the value of Color node?
How to get the value of Value node?

End While


I`ve looked at quite a few examples and none explain how to get the
value of a child node of the current node. Help please.

As long as you know the child element exists it is easy e.g.

For Each fruit As XPathNavigator In
xpathDoc.CreateNavigator().Select("/Data/Fruit")
Dim name = fruit.SelectSingleNode("Name").Value
Dim color = fruit.SelectSingleNode("Color").Value
' use/output name/value here
Next

In the case of the Value element you will then need to check e.g.

For Each fruit As XPathNavigator In
xpathDoc.CreateNavigator().Select("/Data/Fruit")
Dim name As String = fruit.SelectSingleNode("Name").Value
Dim color As String = fruit.SelectSingleNode("Color").Value

Dim valueEl As XPathNavigator = fruit.SelectSingleNode("Value")
If valueEl IsNot Nothing Then
Dim value As String = valueEl.Value
Else
' handle case that no Value child element was found
End If
Next

 

[roidy]

Thanks that`s what I was looking for, I just placed into a function because
not all of the child nodes may exist for each parent node:-

Function ReadChildNode(ByVal navigator As XPathNavigator, _
ByVal nodename As String) As String
Dim result As String = ""
Dim node = navigator.SelectSingleNode(nodename)

If node IsNot Nothing Then
Return node.Value
End If

Return result
End Function


For Each fruit As XPathNavigator In _
xpathDoc.CreateNavigator().Select("/Data/Fruit")
Dim name = ReadChildNode(fruit,"Name")
Dim color = ReadChildNode(fruit,"Color")
Dim value = ReadChildNode(fruit,"Value")
Next

Now the function ReadChildNode takes care of weather the node exists or not.

Thanks again
Rob

 

[roidy]

And of course that should of been simplified to :-

Function ReadChildNode(ByVal navigator As XPathNavigator, _
ByVal nodename As String) As String
Dim node = navigator.SelectSingleNode(nodename)

If node IsNot Nothing Then
Return node.Value
End If

Return Nothing
End Function

Thanks that`s what I was looking for, I just placed into a function
because not all of the child nodes may exist for each parent node:-

Function ReadChildNode(ByVal navigator As XPathNavigator, _
ByVal nodename As String) As String
Dim result As String = ""
Dim node = navigator.SelectSingleNode(nodename)

If node IsNot Nothing Then
Return node.Value
End If

Return result
End Function


For Each fruit As XPathNavigator In _
xpathDoc.CreateNavigator().Select("/Data/Fruit")
Dim name = ReadChildNode(fruit,"Name")
Dim color = ReadChildNode(fruit,"Color")
Dim value = ReadChildNode(fruit,"Value")
Next

Now the function ReadChildNode takes care of weather the node exists or
not.

Thanks again
Rob

 

[Tom Shelton]

Thanks that`s what I was looking for, I just placed into a function because
not all of the child nodes may exist for each parent node:-

Function ReadChildNode(ByVal navigator As XPathNavigator, _
ByVal nodename As String) As String
Dim result As String = ""
Dim node = navigator.SelectSingleNode(nodename)

If node IsNot Nothing Then
Return node.Value
End If

Return result
End Function


For Each fruit As XPathNavigator In _
xpathDoc.CreateNavigator().Select("/Data/Fruit")
Dim name = ReadChildNode(fruit,"Name")
Dim color = ReadChildNode(fruit,"Color")
Dim value = ReadChildNode(fruit,"Value")
Next

Now the function ReadChildNode takes care of weather the node exists or not.

Thanks again
Rob

As long as you know the child element exists it is easy e.g.

For Each fruit As XPathNavigator In
xpathDoc.CreateNavigator().Select("/Data/Fruit")
Dim name = fruit.SelectSingleNode("Name").Value
Dim color = fruit.SelectSingleNode("Color").Value
' use/output name/value here
Next

In the case of the Value element you will then need to check e.g.

For Each fruit As XPathNavigator In
xpathDoc.CreateNavigator().Select("/Data/Fruit")
Dim name As String = fruit.SelectSingleNode("Name").Value
Dim color As String = fruit.SelectSingleNode("Color").Value

Dim valueEl As XPathNavigator = fruit.SelectSingleNode("Value")
If valueEl IsNot Nothing Then
Dim value As String = valueEl.Value
Else
' handle case that no Value child element was found
End If
Next

Have you considered Linq-to-XML?

Option Explicit On
Option Strict On
Option Infer On

Module Module1


Sub Main()

Dim data = <Data>
<Fruit>
<Name>Apple</Name>
<Color>Green</Color>
<Value>100</Value>
</Fruit>
<Fruit>
<Name>Orange</Name>
<Color>Orange</Color>
<Value>75</Value>
</Fruit>
<Fruit>
<Name>Plum</Name>
<Color>Purple</Color>
</Fruit>
</Data>

Dim fruits = From fruit In data.Descendants("Fruit") Select _
New With {.Name = fruit.Element("Name").Value, _
.Color = fruit.Element("Color").Value, _
.Value = If(fruit.Element("Value") IsNot Nothing, _
fruit.Element("Value").Value, "N/A")}

For Each fruit In fruits
Console.WriteLine("Name = {0}, Color = {1}, Value = {2}", _
fruit.Name, fruit.Color, fruit.Value)
Next
End Sub

End Module

Just a thought

 

[roidy]

Thanks Tom is that quicker than XPath as the xml files I`m dealing with are
quite large, the fruit data was just a generic example to get my point
across. Also how would you load the xml from a file or from the web instead
of hard coding it into the program?

 

[Tom Shelton]

Thanks Tom is that quicker than XPath as the xml files I`m dealing with are
quite large, the fruit data was just a generic example to get my point
across. Also how would you load the xml from a file or from the web instead
of hard coding it into the program?

My experience with linq to xml is that it is quite fast, though I have not
done any formal benchmarking So, you might want to compare... Just so you
know , you can actually combine XPath with linq-to-xml, so it's not an either
or situation.

As for loading, I used a vb xml litteral for ease of example Look at the
XElement.Load method's overloads. From a local file:

Dim data As XElement = XElement.Load (path)

There are overloads that take XmlReader, TextReader, or String - so, you have
a few options there for reading from the web - something like the following
air-code:

Dim wc As New System.Net.WebClient()
Dim data As XElement = XElement.Load (wc.DownloadString (url))

Anyway, just thought I might give you something else to look at.

 

[roidy]

Thanks Tom, I`ll do some test and see which is quicker.

Rob