Actually I think that it’s not correct that the OptionType cannot be used as a key type. In fact it is similar to a composite type and should be usable as a key iff it’s element can be used as a key. Then we only have to provide an OptionTypeComparator which will compare the elements if they are set. If not, then the None element will be smaller, for example.
@Timur, if you want, then you can file a JIRA issue to add that.
Cheers,
Till
Ok, I can't make Option comparable, so the only way that I see is to translate a key to a Comparable data structure and use it (as it was alluded to in your example above). Thank you for clarification!Thanks,TimurOn Wed, Mar 30, 2016 at 9:22 AM, Chiwan Park <[hidden email]> wrote:Hi Timur,
Sorry for confusing. I meant KeySelector.
`GenericType<T>` could be used as a key type if the `T` implements `Comparable`. For example, `GenericType<Integer>` could be used as a key type but `GenericType<scala.Tuple2>` could not.
About my example in previous mail, the type of key is `Int` because the return type of KeySelector is `Int`. `TypeInformation<Int>` is not generic type.
Regards,
Chiwan Park
> On Mar 31, 2016, at 1:09 AM, Timur Fayruzov <[hidden email]> wrote:
>
> Thank you for your answers, Chiwan! That would mean that a generic type can't be used as a key in general? This is a non-obvious limitation of Flink DSL that I didn't see in documentation.
>
> Could you please elaborate what you mean by KeyExtractor? I see that inside `where` operator an instance of KeySelector is initialized, but I don't see how can I pass a custom KeySelector in.
>
> Thanks,
> Timur
>
> On Wed, Mar 30, 2016 at 12:53 AM, Chiwan Park <[hidden email]> wrote:
> Hi Timur,
>
> Because Option[T] is not comparable type generally (if T is a POJO type), you cannot use Option[T] as a key type. I think you have to implement KeyExtractor to compare objects including Option[T]s.
>
> ```
> case class MyKey(k1: Option[String], k2: Option[String])
>
> val data1 = env.fromElements(MyKey(Some("a"), None), MyKey(Some("a"), Some("c")))
> val data2 = env.fromElements(MyKey(Some("b"), None), MyKey(Some("a"), Some("c")))
>
> data1.join(data2)
> .where(_.hashCode())
> .equalTo(_.hashCode()).apply {
> (left: MyKey, right: MyKey) => (left, right)
> }.print()
> ```
>
> Note that the approach in example (using hashCode()) cannot be applied to sort task.
>
> Regards,
> Chiwan Park
>
> > On Mar 30, 2016, at 2:37 AM, Timur Fayruzov <[hidden email]> wrote:
> >
> > There is some more detail to this question that I missed initially. It turns out that my key is a case class of a form MyKey(k1: Option[String], k2: Option[String]). Keys.SelectorFunctionKeys is performing a recursive check whether every element of the MyKey class can be a key and fails when encountering an Option.
> >
> > Is it possible to work around this situation without giving up Options? Inability to use Options in Domain objects could be really frustrating.
> >
> > Thanks,
> > Timur
> >
> > On Tue, Mar 29, 2016 at 10:19 AM, Timur Fayruzov <[hidden email]> wrote:
> > Hello,
> >
> > I'm evaluating Flink and one thing I noticed is Option[A] can't be used as a key for coGroup (looking specifically here: https://github.com/apache/flink/blob/master/flink-scala/src/main/scala/org/apache/flink/api/scala/typeutils/OptionTypeInfo.scala#L39). I'm not clear about the reason of this and appreciate if someone can explain.
> >
> > Thanks,
> > Timur
> >
>
>
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