XPath: Selecting a node based on another nodes value

Question

I am trying to use a single XPath expression to select a node that has a child node which matches another node in the document.

A match would mean that ALL attributes of the node are the same. So if a node was being compared with several attributes doing individual attribute comparisons would be unmaintainable.

As an example given the following:

<Network>
    <Machines>
        <Machine Name = "MyMachine">
            <Services>
                 <ServiceDetails Description="MyService" Executable="c:\Myservice.exe" DisplayName="My Service" Version="5"/>
            </Services>
        </Machine>
        ...
    </Machines>
    <Services>
        <Service Name = "Service1">
            <ServiceDetails Description="MyService" Executable="c:\Myservice.exe" DisplayName="My Service" Version="5"/>
        </Service>
        ...
    </Services>
</Network>

I want to get the service node from Services based on the ServiceDetails listed under MyMachine.

I thought it would look something like:

//Services/Service[ServiceDetails = //Machines/Machine[@Name='MyMachine']/ServiceDetails]

but it doesn't seem to work. I suspect the '=' operator isn't handling the node comparison correctly. I think there are some XPath 2.0 Methods that might work but I am using .NET 4.0 (System.XML namespace) I do not know if I can use them. If XPath 2.0 methods would help here I would really appreciate an explanation on how to use them in .Net 4.0.

Thanks

Are you trying to get the <Service> under <Services> by matching the @Description attributes from both <ServiceDetails>? (This would work in that case: /Network/Services/Service[ServiceDetails/@Description = /Network/Machines/Machine[@Name='MyMachine']/Services/ServiceDetails/@Description] ) — Daniel Haley
– Daniel Haley, Commented Sep 21, 2011 at 23:39

Dimitre Novatchev · Accepted Answer · 2011-09-22 01:28:19Z

4

Use:

/*/Services/Service
            [ServiceDetails/@Description 
            = 
             /*/Machines/Machine[@Name = "MyMachine"]
                          /Services/ServiceDetails/@Description
            ]

answered Sep 22, 2011 at 1:28

Dimitre Novatchev

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6 Comments

Dimitre Novatchev Over a year ago

@DevNull: Absolutely -- I saw your comment and decided to give my answer -- when I wrote it completely, I saw that it is almost identical to the expression in your comment. However, it deserves to be an answer -- not a comment. Please, create an answer with this expression, then I'll delete mine :)

Daniel Haley Over a year ago

I was hoping the OP would clarify the question before I answered since the XML example doesn't match the explanation of what was trying to be matched. One answer is sufficient; I will just upvote yours since I'm in agreement. :-)

Dimitre Novatchev Over a year ago

Thanks -- in this case I will have a look at all your answers -- sure there will be some good one I hadn't seen before that I could upvote.

AAADad Over a year ago

Thanks for the reply but the comparison for the question is regarding the entire node. In the example above I would want to make sure the Description and Version were both correct. Given your examples I might be able to concatenate the attribute comparisons but that would quickly become unmanageable. Is there a way to find out if the entire node matches? However, if there are several attributes or children to this node these expressions would get extremely large rather quickly. Is there a way to check if the nodes match rather than walk through each attribute and child?

Dimitre Novatchev Over a year ago

@AAADad: You need to define what is meant by "entire nodes match". There is a term "node equality" and in XPath 2.0 there is a finction deep-equal(). If you need only "shallow equality" (attribute count names and corresponding values to be identical, I think this can be done with an XPath expression.

|

Yogib · Accepted Answer · 2020-09-01 08:26:46Z

0

Try this will validate all attribute values are equal in both the elements then it is true:

/Network[(descendant::ServiceDetails/@Description = /Network//Machine[@Name = "MyMachine"]/Services/ServiceDetails/@Description) and (descendant::ServiceDetails/@Executable = /Network//Machine[@Name = "MyMachine"]/Services/ServiceDetails/@Executable) and (descendant::ServiceDetails/@DisplayName = /Network//Machine[@Name = "MyMachine"]/Services/ServiceDetails/@DisplayName) and (descendant::ServiceDetails/@Version = /Network//Machine[@Name = "MyMachine"]/Services/ServiceDetails/@Version)]

answered Sep 1, 2020 at 8:26

Yogib

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