topic Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow. in Talend Studio

'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

schwarben — Wed, 19 May 2021 12:42:29 GMT

I still experience troubles using tJavaFlex component. Using a main flow as an input, sometimes everything runs smoothly but there are cases when the tJavaFlex only gets null values in all fields. I managed to find a workaround by using a tFlowToIterate component to transcode the main flow in an iterate flow, but I would like to understand what is happening here.

Why is tJavaFlex sometimes ok with main flows, and why sometimes it gets only null values ?
Why using an iterate flow helps ?
And finaly, I realized I don't really get what an iterate flow does and when to use it compared to a main flow.

Any explanation on any of these topics would be greatly appreciated.

Thanks !

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

gjeremy1617088143 — Wed, 19 May 2021 13:31:28 GMT

Hi, why are you using tJavaFlex ?

Could you send screens of the tJavaFlex ?

and also screens of the tFixedFlowinput.

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Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

gjeremy1617088143 — Wed, 19 May 2021 15:17:40 GMT

flow to iterate will execute the rest of the subjob after the iterate link for one iteration of the main flow, so if you have 3 rows in the main flow it will execute the rest 3 times (one for each row of the main flow). It can also stock in globalVar the value of the fields of one row. So you can reuse them at each moment of the iteration.

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

schwarben — Wed, 19 May 2021 15:40:35 GMT

Hello Jeremy, and thanks for your interest.

I typically use a tJavaFlex when I need to "insert" lines in a flow. This can happen in various cases.

In the toy exemple above I have a flow with three String fields (N, P, T). The last field contains a coma separated list of tokens and I want a new line for each token : (N, P, S) where N an P are simply repeated and S contains the token extracted from T.

So, a stream composed of these two lines :

[("x", "y", "0"), ("a" ,"b" , "1,2,3")]

Would result in 4 lines :

[("x","y","0"), ("a","b","1"), ("a","b","2"), ("a","b","3")]

The code seems straightforward, tell me if I misunderstood something.

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

gjeremy1617088143 — Wed, 19 May 2021 16:37:56 GMT

ok just use the tNormalize component , you don't have to use a tJavaflex for this.

tAggegateRow -->main-->tNormalize-->main -->the rest of the job

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Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

schwarben — Thu, 20 May 2021 06:34:06 GMT

Makes perfect sense. Thanks.

Actually, everythink became clear when my last component in the subjob was a file writer. With an iterate, unless I specifically ask for an appending behaviour, the file is overwritten at each iteration.

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

schwarben — Thu, 20 May 2021 06:50:56 GMT

Thanks for pointing out the tNormalize, I actually didn't know that component.

That being said in my today's job, while I need to "normalizie" a column I also need to mute others. Let's say each line contains shopping informations such as the id of the buyer, total shopping price and the coma separated list of purchased items. Even though I don't have the detailed price for each item I need to render a line per item, but when doing so I would like to keep the other fields only on the first line and mute them for the remainig lines.

("bob", "10$", "cake,tea")

-->

("bob", "10$", "cake")

(, , "tea")

tJavaFlex still seems a natural way to perform that.

Furtermore, last time I used a tJavaFlex I had to deal with something a bit more tricky where a part of the job was about storing manager related information in a HashMap, and the other part of the job was about running through this HashMap to extract and list this "per-manager" information. To date I still can't see any other way to do that than using a tJavaFlex.

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

schwarben — Thu, 20 May 2021 07:13:14 GMT

All that aside, do you have any idea if an explanation to why tJavaFlex would read null values from a main flow ? I can provide a toy example if needed.

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

gjeremy1617088143 — Thu, 20 May 2021 07:27:45 GMT

for the tJavaflex i think it's because you use the for clause in the begining and not in the loop, the beginning is launched at first and then it loop for each iteration of the main row in the main part of the tJavaflex.Thats why it's working with tflowtoiterate.

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

gjeremy1617088143 — Thu, 20 May 2021 07:33:01 GMT

you could use tnormalize to separate the values then add an order number with a sequence by exemple and then set to null each values for N and P if order is different to 1.

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

schwarben — Thu, 20 May 2021 07:45:28 GMT

This actually was my first idea, but I didn't find how to do that. I was expecting to do that with a 'rank' operation in the tAggregateRow component to emulate the row_number() function in SQL, but there is none.

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

schwarben — Thu, 20 May 2021 07:46:35 GMT

Thank you ! Thank you ! Thank you !

Now I will be able to sleep !

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

gjeremy1617088143 — Thu, 20 May 2021 07:55:36 GMT

my idea : tflowtoiterate --> iterate -->tjava with a globalMap.put (name counter type int set to 0 )--> on component ok -->rowgenerator with the globalvar of the tflowtoiterate --> main --> tnormalize --> tjavarow with a new column (named order value : counter +1 --> tjavarow (if value of counter !=1 then null for N and P)

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

gjeremy1617088143 — Thu, 20 May 2021 07:56:51 GMT

Ps you could do the both tjavarow code in one like --> (if value of counter + 1 !=1 then null for N and P else N = N ,P =P)

Re: 'null' values received when using a tJavaFlex with a main flow. Fixed by using an iterate flow.

gjeremy1617088143 — Thu, 20 May 2021 08:05:14 GMT

so good night 🙂