Good point. Do you think there's any value to adding a transform that enriches a PCollection with the timestamp? The transform could also take a PCollection and make one of its Instant members the timestamp.
On Tue, May 17, 2016 at 5:51 PM Ben Chambers <[email protected]> wrote: > DoFn is not a functional interface, so lambdas won't work with it. If you > look at MapElements and FlatMapElements, these are transforms built on top > of ParDo that allow passing a lambda. Unfortunately, due to issues with > type erasure and Java generics, when using a lambda it is necessary to > specify the output types as well. You can see an example of this in the > java8tests: > > > https://github.com/apache/incubator-beam/blob/master/sdks/java/java8tests/src/test/java/org/apache/beam/sdk/transforms/MapElementsJava8Test.java#L49 > > Unfortunately, this still won't work well for your use case since the > lambda doesn't have access to the timestamp. > > On Tue, May 17, 2016 at 5:41 PM Jesse Anderson <[email protected]> > wrote: > >> Is there a way to create a DoFN with a lambda function? The DoFN class >> itself should support it, but the overloading of the ParDo.of causes >> ambiguity for a lambda function. Is there a different way to accomplish >> this? >> >> To answer the why would you want this: >> >> static class EnrichWithTimestampFN extends DoFn<KV<String, Long>, >> KV<String, KV<Instant, Long>>> { >> @Override >> public void processElement(DoFn<KV<String, Long>, KV<String, >> KV<Instant, Long>>>.ProcessContext context) throws Exception { >> context.output(KV.of(context.element().getKey(), >> KV.of(context.timestamp(), context.element().getValue()))); >> } >> } >> >> This is a DoFN that I wrote to enrich a PCollection with a the time >> (Instant). I need the access to the ProcessContext to get the timestamp. >> This would be much easier expressed with a lambda. >> >> Thanks, >> >> Jesse >> >
