[
https://issues.apache.org/jira/browse/FLINK-6276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15960407#comment-15960407
]
Luke Hutchison commented on FLINK-6276:
---------------------------------------
[~Zentol] how does my code throw away more information than Java already throws
away because of type erasure? Why does the type hint not work?
To be clear, there are several issues here:
# The {{Unknown Error. Type is null.}} message is not at all helpful.
# The {{The return type of function 'join(TestMain.java:23)' could not be
determined automatically}} message gives the wrong reason for the problem (it
is not the return type of {{join()}} that is the problem).
# The suggested solution {{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}} doesn't work for
generics.
> 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.)
--
This message was sent by Atlassian JIRA
(v6.3.15#6346)
