question Re: Preserving the parent element in XML document with XMLReader in Support Questions

Preserving the parent element in XML document with XMLReader

ChuckE — Fri, 29 Jul 2022 06:13:17 GMT

When using the XMLReader service, how do you retain the outermost parent element of an XML document so when I convert it to JSON I have the outermost element in the JSON version too?

For example, given the following XML document how do I capture the "<a>" element rather than just the "<b>" element?

<a>
  <b>45</b>
</a>

What I want:

{"a": {"b":45}}

What I get:

{"b":45}

Re: Preserving the parent element in XML document with XMLReader

SAMSAL — Fri, 29 Jul 2022 17:42:57 GMT

Hi,

Im not sure this can be fixed by changing some configuration on what you have wither on the processor or the service level. Since the root element is not considered in the conversion from xml to Json, as workaround you can surround your xml with arbitrary root element with the ReplaceText Processor before the ConvertRecrod Processor:

Search Value: (?s)(^.*$)
Replacement Value: <root>$1</root>
Evaluation Mode: Entire Text

This will output the following xml:

<root>n<a>
  <b>45</b>
</a>
n</root>

And After ConvertRecord Prceossor :

{"a": {"b":45}}

Hope that helps. If it does, please Accept Solution.

Thanks

Re: Preserving the parent element in XML document with XMLReader

ChuckE — Mon, 01 Aug 2022 14:26:52 GMT

Thank you SAMSL for your response. In the interest of scalability I was trying to avoid performing text manipulations. I ultimately decided to go with an XSLT transform since this processor is optimized for performing these types of operations, making it more scalable. I wanted to verify there wasn't an option within the XMLReader that I was missing, but it seems not.

On a side note, as an intellectual curiosity I also tried using the QueryRecord processor to see if I could select the outermost element in a query and slap wrapper text around it. But it seems there is no way to perform this task with an XMLReader because it can't discern the schema of the data, so "select * from flowfile" is the only thing that works apparently.

Re: Preserving the parent element in XML document with XMLReader

araujo — Mon, 01 Aug 2022 21:57:26 GMT

@ChuckE

Do your XML messages conform to defined a schema?

Cheers,

André

Re: Preserving the parent element in XML document with XMLReader

ChuckE — Tue, 02 Aug 2022 00:30:25 GMT

Yes, I validate the incoming xml with a strongly typed xsd.

Re: Preserving the parent element in XML document with XMLReader

araujo — Wed, 03 Aug 2022 05:20:16 GMT

@ChuckE ,

You can use a JoltTransformRecord processor to perform the conversion to JSON and, at the same time, add the root node back to it.

The JOLT specification I used is this:

{ "*": "a.&" }

Cheers,

André

Re: Preserving the parent element in XML document with XMLReader

ChuckE — Wed, 03 Aug 2022 05:41:42 GMT

This seems like a good idea. I'll give this a try and test the performance against the XSLT transform. I've never used the JOLT processors before so this will be a good opportunity to experiment with one. Thanks for the idea.

Re: Preserving the parent element in XML document with XMLReader

araujo — Wed, 03 Aug 2022 05:43:20 GMT

I'm also curious about the performance difference. If you could report your results here, I'd appreciate!

Cheers,

André

Re: Preserving the parent element in XML document with XMLReader

ChuckE — Wed, 03 Aug 2022 17:13:40 GMT

I've since discovered a super easy way to resolve this. Simply using the XMLRecordSetWriter does EXACTLY what I was looking for.

Re: Preserving the parent element in XML document with XMLReader

SAMSAL — Thu, 04 Aug 2022 02:24:50 GMT

Can you explain how did you resolve it with XMLRecrodSetWriter? Thanks

Re: Preserving the parent element in XML document with XMLReader

araujo — Thu, 04 Aug 2022 02:33:45 GMT

Ahh! Good catch, @ChuckE !! So simple!

Re: Preserving the parent element in XML document with XMLReader

ChuckE — Thu, 04 Aug 2022 02:59:53 GMT

I create an XMLRecordSetWriter in the Controller Services, then using a ConvertRecord processor I'm able to read the xml record and then immediately write it out with a new root tag, which I can then pass to my next processor. I discovered this when I was reading the documentation for the XMLRecordSetWriter. Very first line in the documentation. 😃

https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi/nifi-record-serialization-services-nar/1.7.0/org.apache.nifi.xml.XMLRecordSetWriter/index.html