How to get the UserName from User Id in a aggregate column function or a rule for filter

Question

a!queryEntity(
 entity: cons!PF_ENTITY_VW_REQUEST,
 query: a!query(
 aggregation: a!queryAggregation(
 aggregationColumns: {
 a!queryAggregationColumn(field: "RequestUserID", isGrouping: true),
 a!queryAggregationColumn(
 field: "RecordID",
 isGrouping: false,
 aggregationFunction: "COUNT"
 )
 }
 ),
 logicalExpression: a!queryLogicalExpression(
 operator: "AND",
 filters: {
 a!queryFilter(field: "RecordID", operator: "not null"),
 if(
 isnull(ri!RequestUserId),
 {},
 a!queryFilter(
 field: "RequestUserID",
 operator: "=",
 value: ri!RequestUserId
 )
 ),
 if(
 isnull(ri!activeStatus),
 {},
 a!queryFilter(
 field: "ActiveStatus",
 operator: "=",
 value: ri!activeStatus
 )
 ),
 if(
 isnull(ri!RecordID),
 {},
 a!queryFilter(
 field: "RecordID",
 operator: "=",
 value: ri!RecordID
 )
 )
 }
 ),
 pagingInfo: if(
 isnull(ri!pagingInfo),
 a!pagingInfo(startIndex: 1, batchSize: - 1),
 ri!pagingInfo
 )
 )
) 
 Hi Appian team, 
 Please check above code return for rule expression, it returns two fields one is RequestUserID and other is recordID. I want to fetch Username from UserID which means I have to get one more field as output that is UserName which I should get from user ID. I know there is user() function in-Build, but i do not know where i can use it to fetch username from RequestUserID field. 
 Can anyone of you help me solve this issue? 
 
 Thanks 
 Sunu Sam

sunus0001 · Accepted Answer

thanks for your help...finally its working i have written a rule to fetch username from user ID and called it where am using it.