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https://issues.apache.org/jira/browse/FLINK-2220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15291048#comment-15291048
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ASF GitHub Bot commented on FLINK-2220:
---------------------------------------
Github user gallenvara closed the pull request at:
https://github.com/apache/flink/pull/1940
> Join on Pojo without hashCode() silently fails
> ----------------------------------------------
>
> Key: FLINK-2220
> URL: https://issues.apache.org/jira/browse/FLINK-2220
> Project: Flink
> Issue Type: Bug
> Affects Versions: 0.9, 0.8.1
> Reporter: Marcus Leich
>
> I need to perform a join using a complete Pojo as join key.
> With DOP > 1 this only works if the Pojo comes with a meaningful hasCode()
> implementation, as otherwise equal objects will get hashed to different
> partitions based on their memory address and not on the content.
> I guess it's fine if users are required to implement hasCode() themselves,
> but it would be nice of documentation or better yet, Flink itself could alert
> users that this is a requirement, similar to how Comparable is required for
> keys.
> Use the following code to reproduce the issue:
> public class Pojo implements Comparable<Pojo> {
> public byte[] data;
> public Pojo () {
> }
> public Pojo (byte[] data) {
> this.data = data;
> }
> @Override
> public int compareTo(Pojo o) {
> return UnsignedBytes.lexicographicalComparator().compare(data,
> o.data);
> }
> // uncomment me for making the join work
> /* @Override
> public int hashCode() {
> return Arrays.hashCode(data);
> }*/
> }
> public void testJoin () throws Exception {
> final ExecutionEnvironment env =
> ExecutionEnvironment.createLocalEnvironment();
> env.setParallelism(4);
> DataSet<Tuple2<Pojo, String>> left = env.fromElements(
> new Tuple2<>(new Pojo(new byte[] {0, 24, 23, 1, 3}), "black"),
> new Tuple2<>(new Pojo(new byte[] {0, 14, 13, 14, 13}), "red"),
> new Tuple2<>(new Pojo(new byte[] {1}), "Spark"),
> new Tuple2<>(new Pojo(new byte[] {2}), "good"),
> new Tuple2<>(new Pojo(new byte[] {5}), "bug"));
> DataSet<Tuple2<Pojo, String>> right = env.fromElements(
> new Tuple2<>(new Pojo(new byte[] {0, 24, 23, 1, 3}), "white"),
> new Tuple2<>(new Pojo(new byte[] {0, 14, 13, 14, 13}),
> "green"),
> new Tuple2<>(new Pojo(new byte[] {1}), "Flink"),
> new Tuple2<>(new Pojo(new byte[] {2}), "evil"),
> new Tuple2<>(new Pojo(new byte[] {5}), "fix"));
> // will not print anything unless Pojo has a real hashCode()
> implementation
>
> left.join(right).where(0).equalTo(0).projectFirst(1).projectSecond(1).print();
> }
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