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From "Gabor Gevay (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLINK-2447) TypeExtractor returns wrong type info when a Tuple has two fields of the same POJO type
Date Fri, 31 Jul 2015 07:59:04 GMT
Gabor Gevay created FLINK-2447:
----------------------------------

             Summary: TypeExtractor returns wrong type info when a Tuple has two fields of
the same POJO type
                 Key: FLINK-2447
                 URL: https://issues.apache.org/jira/browse/FLINK-2447
             Project: Flink
          Issue Type: Bug
            Reporter: Gabor Gevay


Consider the following code:

DataSet<FooBarPojo> d1 = env.fromElements(new FooBarPojo());
		DataSet<Tuple2<FooBarPojo, FooBarPojo>> d2 = d1.map(new MapFunction<FooBarPojo,
Tuple2<FooBarPojo, FooBarPojo>>() {
			@Override
			public Tuple2<FooBarPojo, FooBarPojo> map(FooBarPojo value) throws Exception {
				return null;
			}
		});

where FooBarPojo is the following type:
public class FooBarPojo {
	public int foo, bar;
	public FooBarPojo() {}
}

This should print a tuple type with two identical fields:
Java Tuple2<PojoType<FooBarPojo, fields = [bar: Integer, foo: Integer]>, PojoType<FooBarPojo,
fields = [bar: Integer, foo: Integer]>>

But it prints the following instead:
Java Tuple2<PojoType<FooBarPojo, fields = [bar: Integer, foo: Integer]>, GenericType<FooBarPojo>>

Note, that this problem causes some co-groups in Gelly to crash with "org.apache.flink.api.common.InvalidProgramException:
The pair of co-group keys are not compatible with each other" when the vertex ID type is a
POJO, because the second field of the Edge type gets to be a generic type, but the POJO gets
recognized in the Vertex type, and getNumberOfKeyFields returns different numbers for the
POJO and the generic type.

The source of the problem is the mechanism in TypeExtractor that would detect recursive types
(see the "alreadySeen" field in TypeExtractor), as it mistakes the second appearance of FooBarPojo
with a recursive field.

Specifically the following happens: createTypeInfoWithTypeHierarchy
starts to process the Tuple2<FooBarPojo, FooBarPojo> type, and in line 434 it calls
itself for the first field, which proceeds into the privateGetForClass case which correctly
detects that it is a POJO, and correctly returns a PojoTypeInfo; but in the meantime in line
1191, privateGetForClass adds PojoTypeInfo to "alreadySeen". Then the outer createTypeInfoWithTypeHierarchy
approaches the second field, goes into privateGetForClass, which mistakenly returns a GenericTypeInfo,
as it thinks in line 1187, that a recursive type is being processed.

(Note, that if we comment out the recursive type detection (the lines that do their thing
with the alreadySeen field), then the output is correct.)



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