Let's say i've just parsed someone else's XML document which is a response to an API request. I want to know if a value nested deep inside exists. If my API request worked, it will be in the same place every time. If my API request fails, the root of the XML is very different.

If I try <cfif structKeyExists(myStruct.level1.level2.level3, 'myTarget')> on a failed api request, I get the fatal error: Element LEVEL1.LEVEL2 is undefined in MYSTRUCT.

Of course, I could try to depend on the root level of the XML telling me of success or failure, and not looking for the result if it failed, but... barring that solution, what should i do?

Do i need to check for the existence of each level of the struct? As in:

<cfif structKeyExists(myStruct, 'level1') 
  and structKeyExists(myStruct.level1, 'level2') 
    and structKeyExists(mySt开发者_如何学编程ruct.level1.level2, 'level3') 
      and structKeyExists(myStruct.level1.level2.level3, 'myTarget')>
<!--- ... --->
</cfif>

This is not a real-world problem, this is just something i've faced too many times. Please don't tell me solutions that involve changing the API or solutions like those in the third paragraph.

Thanks!

edit: i should have mentioned why i can't use isDefined() - some of the keys do not have syntactically valid names, so isDefined() throws an error, eg myStruct.level1[42].level3

XMLSearch

I would use the parsed XML document (i.e. xmlDoc) and XMLSearch:

<cfset xmlDoc = xmlParse(responseData)>
<cfset nodes = XmlSearch(xmlDoc, '/level1/level2/level3/myTarget')>
<cfif arrayLen(nodes)>
    <!--- do something, you have the "nodes" array to work with too --->
</cfif>

xpath for XMLSearch() assumes the structure keys are nodes. You would need to modify accordingly if, for instance, 'myTarget' is an attribute of a node.

StructFindKey

Another way of doing this would be StructFindKey.

<cfset result = structFindKey(myStruct, "myTarget")>
<cfif arrayLen(result) AND result.path EQ "level1.level2.level3">
    <!--- do something --->
</cfif>

Conclusion

Haven't tested, but I believe either will be faster than using IsDefined() or a try-catch block. Has the advantage over XMLValidate() of not needing a DTD. And, even with a DTD, the node you want may be defined as optional, so it could still validate.

You could validate the XML against a DTD to make sure the document was in the right format. XmlParse() and XmlValidate() both take a DTD as a parameter.

<cfset validateResult = XmlValidate(myXmlDocument, myDTD)>
<cfif validateResult.status>
    <!--- xml is valid continue processing --->
<cfelse>
    <!--- xml did not validate handle the error --->
</cfif>

Personally I wouldn't go crazy checking for every level of a 'deep' structure like this. I would presume that if the top level exists the rest of the document will be as you expect, and I'd just address the document from there.

If you wanted you could perhaps try to address the value in your struct and wrap it in a try/catch. That way you can handle any errors at any 'level' in the same way.

<cftry>

  <cfset myVar = myStruct.level1.level2.level3 />

<cfcatch type="any">
  <!--- Handle error --->
</cfcatch>
</cftry>

Hope that helps some.

I know I'm going to get booed off the stage here, but this is where isDefined() can save you a lot of typing:

<cfif isDefined(structKeyExists(myStruct.level1.level2.level3)>
<!--- do something --->
</cfif>

I know this is a year old, but I'm going to put in an answer here. I struggled for a good long time with this one, till I found a simple solution. If I know the structure of the XML already, a simple IsDefined works to test if the node or node attribute exists. I don't think most people know you can do this, or have tried and failed because they didn't include single quotes in the IsDefined function.

So say I grab some user xml from a web service somewhere and want to display the user's ID.

<cfhttp url="https://mycompany.com/mywebservices/getusers" username="me" password="mysecret">
<cfset userXMLDoc = XMLParse(ToString(cfhttp.FileContent).trim())>

<cfif IsDefined('userXMLDoc.Data.Record.User.XmlAttributes.id')>
  <cfdump var="#userXMLDoc.Data.Record.User.XmlAttributes.id#">
<cfelse>
  <cfoutput>Failed: No User ID found</cfoutput>
</cfif>