Camunda Modeler: Access constant column's value in output column in Camunda Modeler UI

Question

I am new in Camunda and I am learning. I want to add a constant column either in the input or output section in Camunda Modeler. and I want to access this constant for some calculations and send the output.

In the below Camunda modeler, I have a column num (Expression: payload.num) and a constant column constant (Expression: constant). I want to send the output by the formula constant*payload.num.

And here is my curl:

curl --location --request POST 'http://localhost:8080/engine-rest/engine/default/decision-definition/key/const_id/evaluate' \
--header 'Content-Type: application/json' \
--data-raw '{
    "variables": {
        "payload": {
            "value": {
                 "num":1
            }
        }
    }
}'

and I am getting this error: In Postman:

{
    "type": "RestException",
    "message": "Cannot evaluate decision const_id:9:6522be72-1cdd-11ee-adea-00ff092b2785: Exception while evaluating decision with key 'null'",
    "code": 0
}

I want to output something like (without passing constant as input):

[
    {
        "output": {
            "value": 5,
        }
    }
]

Error in Camunda Modeler CMD:

Caused by: org.camunda.bpm.dmn.feel.impl.FeelException: FEEL/SCALA-01008 Error while evaluating expression: failed to evaluate expression 'constant': no variable found for name 'constant' 

Please help me where I am doing wrong, or How can I access constant column value either from Input or from one output's column to another output's column? Thanks in advance.

Answer 1

I explored and got the solution (workaround) to achieve this.

We can create the decision table like this:

In that decision table, we have two column names (expression - payload.num) as input and Constant (Expression - constant) as output.

The output will be input in one of the expression table (can call a decision table, but it will return an expression.)

Now, we need to create a decision table but in this, we will return an expression. the expression would be:

{
"result":constant*payload.num
}

This is how we can call API in Postman and get the results: