topic Re: Any good tWriteJSONField tutorials? in Talend Studio

Any good tWriteJSONField tutorials?

PhilHibbs — Tue, 08 Jan 2019 14:21:55 GMT

I'm struggling with anything more than a very simple JSON structure. I can create a JSON that has one array element in it, but as soon as it needs anything more (e.g. an array of questions, each one of which contains an array of answers) I get lost. Are there any good examples of building complex JSON structures with tWriteJSONField components?

Re: Any good tWriteJSONField tutorials?

root — Tue, 08 Jan 2019 16:00:06 GMT

@PhilHibbs, I struggle all the time with this component. Infact, I too just posted another q with some additional specifics I am trying to achieve.
I hope some experts can help us here!
Thanks.

Re: Any good tWriteJSONField tutorials?

sushantV — Tue, 08 Jan 2019 20:36:35 GMT

I'd echo that. Can't seem to create a JSON and call the application APIs. This component is probably super broken. None of my questions on the forum ever got answered.

Re: Any good tWriteJSONField tutorials?

yome1 — Tue, 08 Jan 2019 21:19:00 GMT

Hello,

If you are using the subscription version, perhaps you can take a look to the TalendDataMapper.

Re: Any good tWriteJSONField tutorials?

PhilHibbs — Mon, 14 Jan 2019 13:48:44 GMT

Ok here's my quick notes after some experimentation.

1. For each array in a JSON object, you need a tWriteJSONField component.

2. To build the array:

2a. Add elements for the aggregation key, and set the aggregation key in the Component properties

2b. Add a named element to hold the array, give it a class attribute of array

2c. Add an element whose name is not important, give it a class attribute of object

2d. Set the unnamed object element to be the loop element

3. Follow up immediately with a tExtractJSONField component with a Loop Jsonpath query of "$"

4. Map the aggregation key element(s) and the array element into output fields

Now you have the key fields, and the array in a string. You can then join this flow to other flows for other sets of data, and further build up your JSON in more tWriteJSONField components.

The one peculiar thing that baffles me is, the array that you get out from the tExtractJSONField is a string. Normally, when you map a string into a JSON element, it wraps it in quotes. So if the Name column contains Fred, you get this:

"Name":"Fred"

However, when you map the constructed array to a JSON element, you get something like this, which is exactly what is wanted:

"Children":[{"Name":"Alice","Age":7},{"Name":"Bob","Age":5},{"Name":"Carole","Age":1}]

What I expected to see was this:

"Children":"[{\"Name\":\"Alice\",\"Age\":7},{\"Name\":\"Bob\",\"Age\":5},{\"Name\":\"Carole\",\"Age\":1}]"

Can anyone explain why it is doing what I actually want, rather than what I expected it to do?

Re: Any good tWriteJSONField tutorials?

navds — Wed, 16 Jan 2019 11:34:47 GMT

Yeah, Talend is supposed to be user-friendly but trust me, do yourself a favor and use an org.json.JSONObject instead. Now that I think about all the time I spent figuring out how to this very simple thing in Talend without real documentation (because you know, they need to work more on that), I could have developed a very sophisticated solution using pure java.

Re: Any good tWriteJSONField tutorials?

David_Beaty — Wed, 16 Jan 2019 12:56:36 GMT

I'd echo navds comments.

Anything more than a simple/flat JSON structure, construct it yourself, making copious use of tHashInput/Output components to store the constructed JSON as an object and tAggregateRow in LIST(Object) method.

Re: Any good tWriteJSONField tutorials?

root — Thu, 17 Jan 2019 13:02:50 GMT

Thanks.Could you share a quick example of using org.json.JSONObject with this type of setup? I am not very savvy with using custom java code in tflex/ tjavarow. A quick rundown on how to work through the flows to make the json object will be helpful please.

Thank you.

Re: Any good tWriteJSONField tutorials?

root — Thu, 17 Jan 2019 13:04:44 GMT

wow, thats neat. But, for me, I just discovered that tWriteJsonField would create an array instead of an object when single row is returned... This is baffling.

Re: Any good tWriteJSONField tutorials?

root — Thu, 17 Jan 2019 13:06:03 GMT

Would you be able to share some examples of how to work with this? I am currently in the process of overhauling our web services served via ESB, and would love to learn how to create objects using pure java in Talend. A simple rundown with screenshots or something is appreciated. Thanks.

Re: Any good tWriteJSONField tutorials?

navds — Thu, 17 Jan 2019 14:49:18 GMT

Maybe someone has a better technique but I don't like to use dozens of tLibraryLoad to import external jars. I prefer adding it in routine dependencies. In this basic example, I downloaded manually the jar json-20171018.jar (yeah, I wish this could be done project-wide using maven), created a new routine 'Demo', edit routine libraries to add the jar. Now I have a JSON parser which could be used project-wise. Here, I returned a java.util.Map which should be familiar.

browse on your computer

I hope this helps.

Re: Any good tWriteJSONField tutorials?

davechurchley — Wed, 11 Dec 2019 08:11:28 GMT

Hi Phil

This looks like the kind of thing I need to do. Do you have any screenshots showing how to work through your steps, please?

Thanks
Dave

Re: Any good tWriteJSONField tutorials?

davechurchley — Fri, 13 Dec 2019 13:15:22 GMT

OK, I've got this working now using a tMap instead of the tExtractJSONField component.

Re: Any good tWriteJSONField tutorials?

Nordom_LH — Thu, 27 Feb 2020 18:30:40 GMT

how have you done it?