Multi-Instance loop over JSON array

Camunda 7 Topics Discussion & Questions
1

Hi guys,
Ive used multi-instance loops over java collections, however is it possible to configure a multi-instance task over a single process variable which is effectively a JSON array?

regards

Rob

2

Hi Rob,

I haven’t tried this myself yet. Assuming the JSON array variable is a Spin JSON value, it should be possible to write camunda:collection="${variable.elements()}" in the multi-instance configuration.

Cheers,
Thorben

4 Likes
3

Thanks Thorben,

worked like a charm!

regards

Rob

4

A post was split to a new topic: Multiple REST requests based on JSON array

5

Hi @Webcyberrob,

Could you please give more details how you pass a JSON array in the multi-instance collection?

I have a process variable “order” like the following:
[{“orderID”:1,“orderNo”:“6RETYY”,“orderQty”:2},
{“orderID”:2,“orderNo”:“45RFFS”,“orderQty”:5},
{“orderID”:3,“orderNo”:“34HJYT”,“orderQty”:3}]

(actually I have a list of objects retrieved by the database which I then serialize into a process variable:

ObjectValue ordersDataValue = Variables.objectValue(orderEntities)
                    .serializationDataFormat(Variables.SerializationDataFormats.JSON)
                    .create();
            execution.setVariable("orders",ordersDataValue);

I would like my cardinality to be the size of the array.
What should I write in the collection of the multi-instance task? And what in the “Element Variable”?
And then, in each of the multi-instance, how do I access any property, e.g. OrderQty?

Thanks!

6

@kontrag see: Pattern Review: DMN Looping for Array Input

7

Hi @StephenOTT,

I had already seen that post but there you set the “collection” variable as
var collection = S('{ "collection" : ["System 1", "System 3"] }');

while I I have set it as:
[{“orderID”:1,“orderNo”:“6RETYY”,“orderQty”:2}, {“orderID”:2,“orderNo”:“45RFFS”,“orderQty”:5}, {“orderID”:3,“orderNo”:“34HJYT”,“orderQty”:3}]

Also, you append the values after the DMN task but how can I append the values?

Thanks!

8

@kontrag you need to convert your json array into a Java collection. Hence the use of SPIN + the .elements() function.

[quote="kontrag, post:7, topic:349"] Also, you append the values after the DMN task but how can I append the values? [/quote] When you want to append the values, you need to set a delegate or script on the execution `end` listener of your task so that each instance's end gets updated. Its the same model of the DMN pattern.
9

Any easy way to make the conversion?

Also, I don’t have a multi-instance task like your DMN before my actual multi-instance task.
Why do I need the end listener to update the variable?
Can’t I get it the “combinedResult” variable with the values right after the generation of the collection?

10

@kontrag use the SPIN library in your java delegate to generate a spin object and then do a .elements()

Sorry, this was mistake on my part; i was thinking of another thread.

1 Like
11

Hi again,

I have the following string:

String orders = [{“orderID”:1,“orderNo”:“6RETYY”,“orderQty”:2}, {“orderID”:3,“orderNo”:“34HJYT”,“orderQty”:3}]

How do I convert it into JSON?
I try:

 JsonValue orders = SpinValues.jsonValue(orders).create();
        execution.setVariable("orders", orders);`

but I get an error:
Cannot find serializer for value 'Value 'null' of type 'json''.

Thanks!

12

@kontrag see the spin docs on reading Json string into spin: https://docs.camunda.org/manual/7.7/reference/spin/json/01-reading-json/#reading-json-from-a-string

1 Like
13

Thanks @StephenOTT!

I simply wrote
String orders_str = [{“orderID”:1,“orderNo”:“6RETYY”,“orderQty”:2}, {“orderID”:3,“orderNo”:“34HJYT”,“orderQty”:3}]

SpinJsonNode orders = S(orders_str, json());

and worked :wink:

14

@kontrag, Can you please tell me how you have configured the multiinstance in your bpmn. I am also trying to implement something like this. Also how do you access each object in the json and use them in the bpmn user task? Any help is much appreciated.

15

@ChandruM take a look at Pattern Review: DMN Looping for Array Input

16