Ask Ben: Selecting XML Attributes Given Other XML Attributes

Posted September 19, 2007 at 6:39 PM

Tags: ColdFusion, Ask Ben

Earlier today, someone asked me about searching XML documents in such a way that he only wanted to select a tag attribute if the parent tag had another attribute set to a given value. This is actually a simple task with the use of a Predicate. As a review from my ColdFusion XPath and XmlSearch() presentation, predicates are XPath constructs contained in square brackets that filter the results of the returned nodes. Predicates need to result in a boolean-true in order for the selected node to be returned in the final node set.

In our case, there are two ways we can look at the problem that have slightly different XPath values. We want to:

  • Select an attribute node that is part of a element node that has an attribute of a given value.
  • Select an attribute node that has a sibling attribute node of a given value.

While these might sound like the same thing, and do, in fact, result in the same node set, they require different XPath values. Both of these situations are demonstrated in this example:

 Launch code in new window » Download code as text file »

  • <!--- Define our ColdFusion XML document object. --->
  • <cfxml variable="xmlGirls">
  •  
  • <girls>
  • <girl
  • name="Samantha"
  • age="27"
  • hair="Blonde"
  • />
  • <girl
  • name="Kim"
  • age="32"
  • hair="Brunette"
  • />
  • <girl
  • name="Cindi"
  • age="25"
  • hair="Black"
  • />
  • </girls>
  •  
  • </cfxml>
  •  
  •  
  • <!---
  • Get the Name attribute nodes of all the girls
  • who are brunetted. We are going to be doing this
  • by only looking in girl nodes that have a hair
  • attribute that is brunette.
  • --->
  • <cfset arrNodes1 = XmlSearch(
  • xmlGirls,
  • "//girl[ @hair = 'Brunette' ]/@name"
  • ) />
  •  
  • <!---
  • Get the Name attribute nodes of all the girls
  • who are brunetted. We are going to be doing this
  • by getting all name nodes who have a sibling
  • attribute node, hair, that is Brunette.
  • --->
  • <cfset arrNodes2 = XmlSearch(
  • xmlGirls,
  • "//girl/@name[ ../@hair = 'Brunette' ]"
  • ) />
  •  
  •  
  • <!--- Output the matching nodes. --->
  • <cfdump
  • var="#arrNodes1#"
  • label="Names of Burnette Girls - Method ##1"
  • />
  •  
  • <!--- Output the matching nodes. --->
  • <cfdump
  • var="#arrNodes2#"
  • label="Names of Burnette Girls - Method ##2"
  • />

Notice that in our first ColdFusion XmlSearch() call, our XPath value is first limiting on the Girl node, using a predicate that requires the Hair attribute to be Brunette. Then in our second ColdFusion XmlSearch() call, our predicate is requiring a sibling Hair attribute with no explicit mention of the parent tag (other than by relative relationship).

Running the above tag, we get the two CFDump outputs:


 
 
 

 
ColdFusion XmlSearch() That Uses XPath  
 
 
 

 
 
 

 
ColdFusion XmlSearch() That Uses XPath  
 
 
 

As you can see, both return the proper Name attribute, Kim. Now, is there a difference between the two different XPath values used? From a readability standpoint, I think the first one is better. From a performance standpoint, I am going to assume that the first one is also a better choice. Just as with a SQL WHERE clause, I think in an XPath statement, you are gonna get better performance by putting the most limiting statements first; filtering on the Girl node will result in less Name attribute node evaluations and therefore might perform better.

Hope that helps a bit.

Download Code Snippet ZIP File

Post Comment  |  Ask Ben  |  Other Searches  |  Print Page





Reader Comments

Sep 21, 2007 at 12:17 PM // reply »
15 Comments

Ben,

I was looking at doing this exact same thing. How would it work if I wanted to test/search on two variables say Brunette and age = 32


Sep 21, 2007 at 12:36 PM // reply »
7,572 Comments

@Alan,

XPath supports some AND/OR logic in the predicates:

//girl[ @hair = 'Brunette' and @age = '32' ]/@name

Notice that the "and" is lowercase; this is required. An uppercase AND will not work properly.


Dec 2, 2008 at 9:41 PM // reply »
1 Comments

Thanks for this example. It was exactly what I was looking for. Sometimes it's impossible to use XPath without a resources of many solid examples.


Dec 3, 2008 at 8:01 AM // reply »
7,572 Comments

@John,

Awesome! Glad to help. If you run into any more issues with XPath, please drop me a line and I'd be happy to whip up a good demo or tutorial.


Jan 28, 2009 at 4:19 PM // reply »
14 Comments

Saved me AGAIN! 2 in one day...
it's getting to the point that I go to bennadel.com first, then the cfdocs.
(in most cases google finds Ben's stuff first anyway!)


Jan 28, 2009 at 4:25 PM // reply »
7,572 Comments

@Michael,

Ha ha, that's awesome. Always glad to help!


Jul 21, 2009 at 7:28 AM // reply »
1 Comments

thanks, that was very helpful


Mar 11, 2010 at 5:05 AM // reply »
1 Comments

Seems like I'm missing something. If I take this code and put it in a .cfm file and try to run it I get this error:
Detail Premature end of file.
ErrNumber 0
ExceptionMessage Premature end of file.
Message An error occured while Parsing an XML document.


Mar 19, 2010 at 9:10 AM // reply »
7,572 Comments

@Tom,

That's odd. Looks like a malformed XML problem. Make sure you aren't missing any of the ">" closing brackets or something.


Post Comment  |  Ask Ben

Recent Blog Comments
Mar 21, 2010 at 7:40 PM
Is Simulating User-Input Events With jQuery Ever A Good Idea?
A couple of things. One you embed the initial state of of more-info in the CSS. IMHO, that behavior should be in jQuery: moreInfo.hide(); It shows that the behavior your toggling and closing is mor ... read »
Mar 21, 2010 at 3:59 PM
Exploring ColdFusion Component Runtime Class Properties And Serialization
@Elliott, according to Ben's experiment, serializeJSON() doesn't access the private data by default - it doesn't even access the getHair() method - so trying to clone a Girl.cfc via serializeJSON/des ... read »
Mar 21, 2010 at 3:49 PM
Ask Ben: Javascript String Replace Method
I'm confused a bit by what you are asking, but if had this sentence: The color, red, is in the style statement; style: red;. and wanted to remove all or change all of the commas, colons, and semi-c ... read »
Mar 21, 2010 at 3:13 PM
Ask Ben: Javascript String Replace Method
I am trying to make a java program to count the number of times that these punctuation marks occur in a body of text: , : ; . ! - ' " ? / \ I am using this piece to ferret out the commas: numcommas ... read »
Mar 21, 2010 at 11:13 AM
A New Wrist Pain
@chiropractor suwanee, Spoken like someone trying to sell something. Other than for minor, temporary relief from some back pain, chiropractic treatment is nothing but placebo effect and quackery. ... read »
Mar 21, 2010 at 6:32 AM
ColdFusion CFPOP - My First Look
Apologies... The field name in the db for C. is "BounceCode" It stores the code / message which is returned in the email. Sorry for the confusion. ... read »
Mar 21, 2010 at 6:29 AM
ColdFusion CFPOP - My First Look
@Jose Galdamez, Hi Ben and Jose 1st of all.. big thanks to Jose for his Skype chat a few weeks back. Your time was much appreciated. I have come up with a rather unelegant solution to my problem a ... read »
Mar 21, 2010 at 3:42 AM
A New Wrist Pain
Chiropractic treatment is one of the best methods for treating numerous health problems naturally. After years of experience being a chiropractor, I have found that it is a powerful way to solve many ... read »