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 <timur.fairu...@gmail.com> 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 <chiwanp...@apache.org> 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 <timur.fairu...@gmail.com> > > 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 <timur.fairu...@gmail.com> > > 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 > > > >