monitor-table-change-with-sqltabledependency | Get SQL Server notification on record table change | SQL Database library

Given that you are using Observable.takeWhile in your example, I'm assuming that you are using the FSharp.Control.Reactive wrapper to get access to the full range of reactive combinators.

Your approach has some good ideas, such as using takeWhile to wait until you collect all IDs, but the use of mutation is quite unfortunate - it might not even be safe to do this because of possible race conditions.

A nice alternative is to use one of the various scan function to collect a state as the events happen. You can use Observable.scanInit to start with an empty set and add all IDs; followed by Observable.takeWhile to keep accepting events until you have all the IDs you're waiting for. To actually wait (and block), you can use Observable.wait. Something like this: