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Posted to user@flink.apache.org by yunfan123 <yu...@foxmail.com> on 2017/09/11 10:38:55 UTC

Keyed function type erasure problem.

Just small change from PojoExample:
PojoExample.java
<http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/file/t921/PojoExample.java>  
public class PojoExample<KEY> {
        private SelectorContainer<KEY> selectorContainer;
        // KeySelector class like this can't be used in flink !!!
	public static class SelectorContainer<K> implements KeySelector<Word ,K> {
		public KeySelector<Word, K> keySelector;
		public SelectorContainer(KeySelector<Word, K> keySelector) {
			this.keySelector = keySelector;
		}

		@Override
		public K getKey(Word value) throws Exception {
			return keySelector.getKey(value);
		}
	}
        public void run() {
              dataStream.keyed(selectorContainer);
        }
        
}

This will cause:
Type of TypeVariable 'K' in 'class
org.apache.flink.streaming.examples.wordcount.PojoExample$SelectorContainer'
could not be determined. This is most likely a type erasure problem. The
type extraction currently supports types with generic variables only in
cases where all variables in the return type can be deduced from the input
type(s).

org.apache.flink.api.java.typeutils.TypeExtractor.createTypeInfoWithTypeHierarchy(TypeExtractor.java:915)

org.apache.flink.api.java.typeutils.TypeExtractor.privateCreateTypeInfo(TypeExtractor.java:836)

org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:622)

org.apache.flink.api.java.typeutils.TypeExtractor.getKeySelectorTypes(TypeExtractor.java:443)

org.apache.flink.api.java.typeutils.TypeExtractor.getKeySelectorTypes(TypeExtractor.java:436)

org.apache.flink.streaming.api.datastream.KeyedStream.<init>(KeyedStream.java:108)

org.apache.flink.streaming.api.datastream.DataStream.keyBy(DataStream.java:263)

org.apache.flink.streaming.examples.wordcount.PojoExample.execute(PojoExample.java:86)

org.apache.flink.streaming.examples.wordcount.PojoExample.main(PojoExample.java:108)

It sames can't use a class contains the KeySelector ?



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Re: Keyed function type erasure problem.

Posted by yunfan123 <yu...@foxmail.com>.

Thanks



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Re: Keyed function type erasure problem.

Posted by Fabian Hueske <fh...@gmail.com>.

Hi,

The problem is that Flink cannot determine the key type produced by the
KeySelector because the type is a generic.
The type information is lost at runtime due to Java's type erasure.

You can try to implement the ResultTypeQueryable interface with the
KeySelector and tell Flink the key type directly.

Best,
Fabian

2017-09-11 12:38 GMT+02:00 yunfan123 <yu...@foxmail.com>:

> Just small change from PojoExample:
> PojoExample.java
> <http://apache-flink-user-mailing-list-archive.2336050.
> n4.nabble.com/file/t921/PojoExample.java>
> public class PojoExample<KEY> {
>         private SelectorContainer<KEY> selectorContainer;
>         // KeySelector class like this can't be used in flink !!!
>         public static class SelectorContainer<K> implements
> KeySelector<Word ,K> {
>                 public KeySelector<Word, K> keySelector;
>                 public SelectorContainer(KeySelector<Word, K>
> keySelector) {
>                         this.keySelector = keySelector;
>                 }
>
>                 @Override
>                 public K getKey(Word value) throws Exception {
>                         return keySelector.getKey(value);
>                 }
>         }
>         public void run() {
>               dataStream.keyed(selectorContainer);
>         }
>
> }
>
> This will cause:
> Type of TypeVariable 'K' in 'class
> org.apache.flink.streaming.examples.wordcount.
> PojoExample$SelectorContainer'
> could not be determined. This is most likely a type erasure problem. The
> type extraction currently supports types with generic variables only in
> cases where all variables in the return type can be deduced from the input
> type(s).
>
> org.apache.flink.api.java.typeutils.TypeExtractor.
> createTypeInfoWithTypeHierarchy(TypeExtractor.java:915)
>
> org.apache.flink.api.java.typeutils.TypeExtractor.privateCreateTypeInfo(
> TypeExtractor.java:836)
>
> org.apache.flink.api.java.typeutils.TypeExtractor.
> getUnaryOperatorReturnType(TypeExtractor.java:622)
>
> org.apache.flink.api.java.typeutils.TypeExtractor.getKeySelectorTypes(
> TypeExtractor.java:443)
>
> org.apache.flink.api.java.typeutils.TypeExtractor.getKeySelectorTypes(
> TypeExtractor.java:436)
>
> org.apache.flink.streaming.api.datastream.KeyedStream.<
> init>(KeyedStream.java:108)
>
> org.apache.flink.streaming.api.datastream.DataStream.
> keyBy(DataStream.java:263)
>
> org.apache.flink.streaming.examples.wordcount.PojoExample.execute(
> PojoExample.java:86)
>
> org.apache.flink.streaming.examples.wordcount.
> PojoExample.main(PojoExample.java:108)
>
> It sames can't use a class contains the KeySelector ?
>
>
>
> --
> Sent from: http://apache-flink-user-mailing-list-archive.2336050.
> n4.nabble.com/
>