Accumulate Output
For iteration and repeat until true loops, you can accumulate the output of one of the activities in a group by checking the Accumulate Output field. If you check this field, you can select one of the activities in the group, and each time the loop is executed, the selected activity’s output is placed into a list. The list of accumulated output for that activity is stored in a variable whose name is specified in the Output Name field. After the loop exits, this variable can be accessed in the same way other process data can be accessed by other activities.
Because you can accumulate output from only one activity in a group, you should design your group so that only one activity in the group holds the data to accumulate for each iteration. For example, you may want to accumulate a list of customer names from repeated executions of a JDBC Database Query task, or you may wish to accumulate the sum of the amounts for line items in an order.
The output for the selected activity is accumulated each time the activity is executed. Therefore, if you choose to accumulate the output of the same activity used in the condition of a Repeat Until True loop, the activity is executed and the output is added to the list before the condition is checked. In this case, you may wish to use a Mapper activity in the loop to accumulate the output. The Mapper activity is placed after the activity used for the condition of the loop so that the loop exits before the value is accumulated. Alternatively, you can place a Mapper activity outside of the loop to strip out the unwanted value from the output list after the loop exits.