Hi Timur,
You have to use `createTypeInfomation` method in `org.apache.flink.api` package
to create TypeInformation object for Scala-specific objects such as case
classes, tuples, eithers, options. For example:
```
import org.apache.flink.api.scala._ // to import package object
val a: DataSet[Thing] = …
val b: DataSet[Thing] = …
a.coGroup(b)
.where(e => (e.f1, e.f2))
.equalTo(e => (e.f1, e.f2))(createTypeInformation[(String, String)]) {
(left, right) => 1
}.print()
```
Note that Flink creates internally copied 2-tuples consisted of (extracted key
by KeySelector, original value). So there is some performance decrease when you
are using KeySelector.
Regards,
Chiwan Park
> On Mar 31, 2016, at 12:58 AM, Timur Fayruzov <timur.fairu...@gmail.com> wrote:
>
> Thank you Chiwan! Yes, I understand that there are workarounds that don't use
> function argument (and thus do not require implicit arguments). I try to
> avoid positional and string-based keys because there is no compiler
> guarantees when you refactor or accidentally change the underlying case
> classes. Providing a function is the cleanest solution (and arguably is the
> most readable) so it'd be great to make it work.
>
> BTW, TypeInformation.of has an implementation that takes TypeHint
> (https://github.com/apache/flink/blob/master/flink-core/src/main/java/org/apache/flink/api/common/typeinfo/TypeHint.java)
> which, according to documentation, is supposed to be used for generic
> classes, but using it still leads to the same exception.
>
> Thanks,
> Timur
>
>
> On Wed, Mar 30, 2016 at 12:05 AM, Chiwan Park <chiwanp...@apache.org> wrote:
> Hi Timur,
>
> You can use a composite key [1] to compare keys consisting of multiple
> fields. For example:
>
> ```
> val a = env.fromCollection(Seq(Thing("a", "b"), Thing("c", "d")))
> val b = env.fromCollection(Seq(Thing("a", "x"), Thing("z", "m")))
> a.coGroup(b)
> .where(“f1”, “f2”) // Flink compares the values of f1 first, and compares
> the values of f2 if values of f1 are same.
> .equalTo(“f1”, “f2”) { // Note that you must specify same number of keys
> (left, right) => 1
> }
> ```
>
> Composite key can be applied to Scala tuple also:
>
> ```
> val a = env.fromCollection(Seq(("a", "b"), ("c", "d")))
> val b = env.fromCollection(Seq(("a", "x"), ("z", "m")))
> a.coGroup(b)
> .where(0, 1) // Note that field numbers start from 0.
> .equalTo(0, 1) {
> (left, right) => 1
> }
> ```
>
> I hope this helps.
>
> [1]:
> https://ci.apache.org/projects/flink/flink-docs-master/apis/common/index.html#define-keys-for-tuples
>
> Regards,
> Chiwan Park
>
> > On Mar 30, 2016, at 3:54 AM, Timur Fayruzov <timur.fairu...@gmail.com>
> > wrote:
> >
> > Hello,
> >
> > Another issue I have encountered is incorrect implicit resolution (I'm
> > using Scala 2.11.7). Here's the example (with a workaround):
> > val a = env.fromCollection(Seq(Thing("a", "b"), Thing("c", "d")))
> > val b = env.fromCollection(Seq(Thing("a", "x"), Thing("z", "m")))
> > a.coGroup(b)
> > .where(e => e.f1)
> > //.equalTo(e => e) { //this fails to compile because equalTo expects an
> > implicit
> > .equalTo("f1") {
> > (left, right) => 1
> > }
> > However, the workaround does not quite work when key is a tuple (I suspect
> > this applies to other generic classes as well):
> > val a = env.fromCollection(Seq(Thing("a", "b"), Thing("c", "d")))
> > val b = env.fromCollection(Seq(Thing("a", "x"), Thing("z", "m")))
> > a.coGroup(b)
> > .where(e => (e.f1, e.f2))
> > .equalTo(e => (e.f1, e.f2))(TypeInformation.of(classOf[(String,
> > String)])) { (left, right) => 1} // throws InvalidProgramException
> > Here, I try to provide the implicit TypeInformation explicitly, but
> > apparently it's not compatible with the way implicit inference is done.
> > (TypeInformation I generate is GenericType<scala.Tuple2>, while
> > scala.Tuple2<String, String> is expected).
> >
> > Now, I can split this in 2 operations like below:
> > val tmp = a.coGroup(b)
> > .where(e => (e.f1, e.f2))
> > .equalTo(e => (e.f1, e.f2))
> >
> > tmp { (left, right) => 1}
> > but, I would like to avoid adding clutter to my processing logic, and it's
> > not entirely clear to me how this would be scheduled.
> >
> > As an option, I can hash the hell out of my keys like that:
> > a.coGroup(b)
> > .where(e => (e.f1, e.f2).hashCode)
> > .equalTo(e => (e.f1, e.f2).hashCode)(TypeInformation.of(classOf[Int])){
> > (left, right) => 1}
> > but that, again, adds some indirection and clutter, not mentioning the
> > hassle of dealing with collisions (which can be alleviated by using fancy
> > hashes, but I'd like to avoid that).
> >
> > Any insights on what is the way to go here are highly appreciated.
> >
> > Thanks,
> > Timur
>
>
