check if xml node does not exist and do something instead of failing

Question

Given the following XML.

<?xml version="1.0" encoding="UTF-8"?>
<xmldata>
   <Products>
       <ProductCode>M406789</ProductCode>
       <ProductID>858</ProductID>
       <ProductName>M406789 Ignition Box</ProductName>
       <ProductDescriptionShort>&lt;img alt="" src="/v/vspfiles/assets/images/alliance_small.jpg" align="right" /&gt;Ignition Box</ProductDescriptionShort>
       <ListPrice>134.2200</ListPrice>
       <ProductPrice>80.5300</ProductPrice>
       <SalePrice>59.9500</SalePrice>
   </Products>
</xmldata>

This is the relevant part of a script.

Set xNewDoc = xData.responseXML 'ResponseXml returns DOMDocument object

Set ProductCode = xNewDoc.SelectSingleNode("//ProductCode")
Set ListPrice = xNewDoc.SelectSingleNode("//ListPrice")

x=Len(ListPrice.Text)
newlp = Left(ListPrice.Text,x-2)

Set ProductPrice = xNewDoc.SelectSingleNode("//ProductPrice")
x=Len(ProductPrice.Text)
newpp = Left(ProductPrice.Text,x-2)

Set SalePrice = xNewDoc.SelectSingleNode("//SalePrice")
x=Len(SalePrice.Text)
newsp = Left(SalePrice.Text,x-2)

Set ProductName = xNewDoc.SelectSingleNode("//ProductName")

If the above xml that is loaded is missing and of the nodes (lets say "SalePrice") the script will fail. How can I test to see if the node exists so it doesn't fail. I saw something on this on Stack in the past but can't seem to find it.

Solution 1

After setting getting a node from the XML, apply an Is Nothing check around the rest:

newpp = 0 'Initialize with a default value
Set ProductPrice = xNewDoc.SelectSingleNode("//ProductPrice")
If Not ProductPrice Is Nothing Then
    x=Len(ProductPrice.Text)
    newpp = Left(ProductPrice.Text,x-2)
End If

Solution 2

You can just do an If Not ... Is Nothing check every time you use the variable, like so:

Set ListPrice = xNewDoc.SelectSingleNode("//ListPrice")

If Not ListPrice Is Nothing Then
    x=Len(ListPrice.Text)
    newlp = Left(ListPrice.Text,x-2)
End If

Set ProductPrice = xNewDoc.SelectSingleNode("//ProductPrice")

If Not ProductPrice Is Nothing Then
    x=Len(ProductPrice.Text)
    newpp = Left(ProductPrice.Text,x-2)
End If

Comments

[user357034]

While this works I am trying to decide in my situation if I want newpp to = 0 or leave it undefined as with Paul's code.

[Jon Egerton]

The only issue with leaving it undefined is that you may find other errors later on when you try to use that variable if it is of the wrong type. The other aspect is that it may remain set from a previous loop through if you're handling more than on xml doc - so carrying data in from other instances of the product. Its generally not great to no initialize things as it often leads to difficult or obscure bugs.