Sequence contains no elements

[Todd Nine]

Hey guys,

  I've implemented my on OnSubscribe function that wraps a Astyanax iterator and emits Observables.  This works well, however, if the user issues a query that has no results, my subscription immediately emits .onCompleted().  When doing this, it throws an exception below.

java.lang.IllegalArgumentException: Sequence contains no elements

at rx.operators.OperationSingle$1$1.onCompleted(OperationSingle.java:64)

at rx.Observable$28.onCompleted(Observable.java:7002)

Here is the link to my source.

https://github.com/usergrid/usergrid/blob/51a9ffd9218bdaf4884709fd04bae9c046dc67ec/stack/corepersistence/graph/src/main/java/org/apache/usergrid/persistence/graph/serialization/impl/parse/ObservableIterator.java

Given that there may be no matches in Cassandra, is it possible to avoid this issue?

 

[Dave Ray]

It looks like you have a "single" operator after your Observable which is throwing the exception. I'd expect a similar exception if your Observable emitted more than one result as well.

If you're using BlockingObservable.single() to collect results, maybe try putting a toList() before it.

Dave