Azure stream analytics query - how to set even timestamp based on a javascript udf function? - azure-stream-analytics

Question

I am timestamping data stream input events by a property "TS" in the message. However before I timestamp it using TS, I want to ensure that TS is ISO8601 compliant. If TS is not ISO8601 ocmpliant, I want to use EventEnqueuedUtcTime which is the arrival time of the message as timestamp.
My query looks something like this
SELECT
T.*
FROM
input TIMESTAMP BY PARTITION BY PartitionId TIMESTAMP BY udf.getEventTimestamp(T)
Here udf.getEventTimestamp(T) returns the TS property in message(T) if it is ISO8601-compliant otherwise it will return EventEnqueuedUtcTime( arrival time of message in Iot Hub).
Running this script locally gives me the exception -
Error : Unexpected hosted function call
I also tried to use CASE construct to accomplish this
SELECT
T.*
FROM
input TIMESTAMP BY PARTITION BY PartitionId TIMESTAMP BY
CASE
WHEN udf.isValid(T.TS) THEN T.TS
ELSE T.EventEnqueuedUtcTime
END
where udf.isValid(T.TS) returns true if the property TS is a valid ISO8601 compliant timestamp.
Again running this locally returns - Error : Unexpected hosted function call
As per Microsoft Azure docs, After you add a JavaScript user-defined function to a job, you can use the function anywhere in the query, like a built-in scalar function
Does this mean that we cannot use udfs in TIMESTAMP BY and CASE constructs?
Can you suggest any workaround?

Answer 1

At this time we can't use UDF within the TIMESTAMP BY clause.
However we case use TRY_CAST to solve your requirement.
Here's the query with the workaround:
SELECT
T.*
FROM
input PARTITION BY PartitionId TIMESTAMP BY
CASE
WHEN TRY_CAST(T.TS AS DateTime) is not null THEN T.TS
ELSE T.EventEnqueuedUtcTime
END
Let me know if you have any further question.
Thanks,
JS