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https://issues.apache.org/jira/browse/FLINK-6276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15961936#comment-15961936
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Luke Hutchison commented on FLINK-6276:
---------------------------------------
[~sunjincheng121] [~Zentol] I understand that type parameters are not currently
accepted. But why can't the serializer just serialize whatever concrete type it
receives, and deserialize it to the same concrete type on the other end? If the
program typechecks, I don't see why this would be a problem.
Is the issue that the serializer does not currently store the concrete type in
the serialized representation? If so, in the case of generics, the concrete
type should in fact be serialized with the object, so that generics may be
supported. Not supporting generics is a huge shortcoming.
> InvalidTypesException: Unknown Error. Type is null.
> ---------------------------------------------------
>
> Key: FLINK-6276
> URL: https://issues.apache.org/jira/browse/FLINK-6276
> Project: Flink
> Issue Type: Bug
> Components: Core, DataSet API
> Affects Versions: 1.2.0
> Reporter: Luke Hutchison
>
> Quite frequently when writing Flink code, I get the exception
> {{InvalidTypesException: Unknown Error. Type is null.}}
> A small example that triggers it is:
> {code}
> import java.util.ArrayList;
> import java.util.Arrays;
> import java.util.Iterator;
> import java.util.List;
> import org.apache.flink.api.java.DataSet;
> import org.apache.flink.api.java.ExecutionEnvironment;
> import org.apache.flink.api.java.tuple.Tuple2;
> import org.apache.flink.util.Collector;
> public class TestMain {
> @SafeVarargs
> public static <K, V> DataSet<Tuple2<K, List<V>>> join(V
> missingValuePlaceholder,
> DataSet<Tuple2<K, V>>... datasets) {
> DataSet<Tuple2<K, List<V>>> join = null;
> for (int i = 0; i < datasets.length; i++) {
> final int datasetIdx = i;
> if (datasetIdx == 0) {
> join = datasets[datasetIdx]
> .map(t -> {
> List<V> initialList = new ArrayList<>();
> initialList.add(t.f1);
> return new Tuple2<>(t.f0, initialList);
> })
> .name("start join");
> } else {
> join = join.coGroup(datasets[datasetIdx]) //
> .where(0).equalTo(0) //
> .with((Iterable<Tuple2<K, List<V>>> li,
> Iterable<Tuple2<K, V>> ri,
> Collector<Tuple2<K, List<V>>> out) -> {
> K key = null;
> List<V> vals = new ArrayList<>(datasetIdx + 1);
> Iterator<Tuple2<K, List<V>>> lIter =
> li.iterator();
> if (!lIter.hasNext()) {
> for (int j = 0; j < datasetIdx; j++) {
> vals.add(missingValuePlaceholder);
> }
> } else {
> Tuple2<K, List<V>> lt = lIter.next();
> key = lt.f0;
> vals.addAll(lt.f1);
> if (lIter.hasNext()) {
> throw new RuntimeException("Got
> non-unique key: " + key);
> }
> }
> Iterator<Tuple2<K, V>> rIter = ri.iterator();
> if (!rIter.hasNext()) {
> vals.add(missingValuePlaceholder);
> } else {
> Tuple2<K, V> rt = rIter.next();
> key = rt.f0;
> vals.add(rt.f1);
> if (rIter.hasNext()) {
> throw new RuntimeException("Got
> non-unique key: " + key);
> }
> }
> out.collect(new Tuple2<K, List<V>>(key, vals));
> }) //
> .name("join #" + datasetIdx);
> }
> }
> return join;
> }
> public static void main(String[] args) throws Exception {
> ExecutionEnvironment env =
> ExecutionEnvironment.getExecutionEnvironment();
> DataSet<Tuple2<String, Integer>> x = //
> env.fromElements(new Tuple2<>("a", 3), new Tuple2<>("b", 4),
> new Tuple2<>("c", 5));
> DataSet<Tuple2<String, Integer>> y = //
> env.fromElements(new Tuple2<>("b", 0), new Tuple2<>("c", 1),
> new Tuple2<>("d", 2));
> DataSet<Tuple2<String, Integer>> z = //
> env.fromElements(new Tuple2<>("c", 7), new Tuple2<>("d", 8),
> new Tuple2<>("e", 9));
> System.out.println(join(-1, x, y, z).collect());
> }
> }
> {code}
> The stacktrace that is triggered is:
> {noformat}
> Exception in thread "main"
> org.apache.flink.api.common.functions.InvalidTypesException: The return type
> of function 'join(TestMain.java:23)' could not be determined automatically,
> due to type erasure. You can give type information hints by using the
> returns(...) method on the result of the transformation call, or by letting
> your function implement the 'ResultTypeQueryable' interface.
> at org.apache.flink.api.java.DataSet.getType(DataSet.java:174)
> at
> org.apache.flink.api.java.operators.CoGroupOperator$CoGroupOperatorSets.where(CoGroupOperator.java:424)
> at
> com.rentlogic.buildingscores.flink.experimental.TestMain.join(TestMain.java:27)
> at
> com.rentlogic.buildingscores.flink.experimental.TestMain.main(TestMain.java:74)
> Caused by: org.apache.flink.api.common.functions.InvalidTypesException: Input
> mismatch: Unknown Error. Type is null.
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.validateInputType(TypeExtractor.java:1134)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:409)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:349)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.getMapReturnTypes(TypeExtractor.java:164)
> at org.apache.flink.api.java.DataSet.map(DataSet.java:215)
> at
> com.rentlogic.buildingscores.flink.experimental.TestMain.join(TestMain.java:23)
> ... 1 more
> Caused by: org.apache.flink.api.common.functions.InvalidTypesException:
> Unknown Error. Type is null.
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.validateInfo(TypeExtractor.java:1161)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.validateInfo(TypeExtractor.java:1234)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.validateInputType(TypeExtractor.java:1131)
> ... 6 more
> {noformat}
> The code compiles fine, and typechecks. Maybe something is wrong with the
> code; but either way, Flink should report a better error message.
> A separate issue here is that the error message is being reported for the
> wrong function: the problem is not with the return type of
> {{join(TestMain.java:23)}}, it is some internal type (probably for a lambda
> or something) within the function. (It is the {{where}} clause that throws
> the exception.)
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