WSO2 EI/ESB: For loop implementation

Question

I want to implement a simple "for loop" in WSO2 Integration Studio.

For example:

I am implementing a bus-route API. Every bus has 10 different stops. I want to fetch the 10 stops from the back-end service. A normal for-loop for this would be:

for(i=0;i<10;i++)
{
    //back-end call
    <call>
       <endpoint>
          <http method="get" uri-template="https://backend.com/city+i"/>
       </endpoint>
    </call>
}

NOTE: In the above for loop, the back-end call has path parameter like city which should be iterated as city1, city2, city3,..... city9.

How do I implement this in WSO2 EI/ESB Integration Studio?

How are you storing the URLs for the backend calls? Based on that we can try to come up with an idea. — Arunan Sugunakumar, May 14 '20 at 16:09
I have edited the for loop in the question and have also added a NOTE at bottom, please check. I'm not storing the URLs for backend calls anywhere. For backend calls, I'm using Call Mediator inside the http endpoint. Does this answer your doubt? — cracknut, May 14 '20 at 16:56

score 2 · Answer 1 · answered May 14 '20 at 19:35

2

One simple way would be to define a sample payload with the numbers inside an array and iterate through it. (This would work if the number of the iterations are predefined) For eg: [{"value" : 1},{"value" :2},{"value" : 3}, ... ]

Or else you can write a custom class mediator and implement your logic.

Also there is a fun way to implement a while loop with the help of database. http://bsenduran.blogspot.com/2017/08/while-loop-in-wso2-esb.html?m=1

answered May 14 '20 at 19:35

Arunan Sugunakumar

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If I want to define a sample payload manually, like you suggested, which mediator can do that? Can you give me a sample example? – cracknut May 15 '20 at 05:02
1

Use PayloadFactoryMediator. [{"value" : 1},{"value" : 2},{"value" : 3}] – Arunan Sugunakumar May 15 '20 at 06:00
Can I use Iterate mediator inside Iterate mediator? – cracknut May 15 '20 at 08:46
Yes you can https://dzone.com/articles/nested-iterator-wso2-esb – Arunan Sugunakumar May 15 '20 at 10:39
What should be the Iterate expression for the payload factory that you suggested? json-eval($.value) or just $.value? – cracknut May 15 '20 at 11:11
You need to use `json-eval($.value)` – Arunan Sugunakumar May 15 '20 at 15:31
Getting error. `Exception occurred while executing the Iterate Mediator com.jayway.jsonpath.PathNotFoundException: Expected to find an object with property ['value'] in path $ but found 'com.google.gson.JsonArray'. This is not a json object according to the JsonProvider: 'com.jayway.jsonpath.spi.json.GsonJsonProvider'.` – cracknut May 15 '20 at 15:38
1

If you are trying to iterate through the array I have provided, then try `json-eval($)` – Arunan Sugunakumar May 15 '20 at 17:16
Facing issue in using the payload from payload factory in path parameter of back-end call. https://stackoverflow.com/q/61865247/13424730 – cracknut May 18 '20 at 08:16
Do you know how can this be implemented? – cracknut May 18 '20 at 14:53

WSO2 EI/ESB: For loop implementation

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