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From Timur Fayruzov <timur.fairu...@gmail.com>
Subject Re: Why Scala Option is not a valid key?
Date Wed, 30 Mar 2016 16:09:23 GMT
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 <chiwanpark@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.fairuzov@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.fairuzov@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
> >
>
>

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