@PamidiS9 

Can the following be helpful: https://collaborate.pega.com/question/how-call-data-transform-expression-builder

@PamidiS9 

We cannot call data transform directly from expression builder. The link shared by Marc has the steps to call DataTransform from expression builder.

I will reiterate the same here. 

1. Create a data transform

2. Create an activity which calls the above data transform

3. Create a custom function which calls above activity

4. Use this function in the expression builder

Can you specify your requirement to call Data Transform in WHEN rule?

Regards,

Tashika

@PamidiS9   We can use Data Transforms in When rule by building a function that internally calls a DT.

Consider the below scenario where we would like to get particular Return value from DT.

So, our function will be like @GetParamFromTransform("DoesPersonExist","Response")

Data Transform -- DoesPersonExist

Parameter -- Param.Response, being set in DoesPersonExist

Function GetParamFromTransform with 2 Parameters ,transformName and responseParam

PublicAPI tools = null; PRThread thisThread = (PRThread)ThreadContainer.get(); if (thisThread != null)      tools = thisThread.getPublicAPI(); else     throw new PRAppRuntimeException("Pega-RULES", 0, "Unable to obtain current thread");

tools.applyModel(tools.getStepPage(),tools.getParameterPage(),transformName);

return tools.getParamValue(responseParam);