[jira] [Created] (FLINK-5677) Validation layer should check whether field can be used as grouping key

["Timo Walther (JIRA)" <ji...@apache.org>]

Timo Walther created FLINK-5677:
-----------------------------------

             Summary: Validation layer should check whether field can be used as grouping key
                 Key: FLINK-5677
                 URL: https://issues.apache.org/jira/browse/FLINK-5677
             Project: Flink
          Issue Type: Improvement
          Components: Table API & SQL
            Reporter: Timo Walther


When grouping on a GenericType (e.g. {{Object}}). The validation layer does no checking of types. The {{groupBy/keyBy}} of DataSet/DataStream API throws the exception. The validation layer should check this before.

{code}
public static class OuterPojo {
	public Object object = new Object();
}
tEnv.sql("SELECT testing.object FROM testing GROUP BY testing.object")
{code}

leads to 
{code}
Exception in thread "main" org.apache.flink.api.common.InvalidProgramException: This type (GenericType<java.lang.Object>) cannot be used as key.
	at org.apache.flink.api.common.operators.Keys$ExpressionKeys.<init>(Keys.java:270)
	at org.apache.flink.api.common.operators.Keys$ExpressionKeys.<init>(Keys.java:223)
	at org.apache.flink.api.java.DataSet.groupBy(DataSet.java:692)
	at org.apache.flink.table.plan.nodes.dataset.DataSetAggregate.translateToPlan(DataSetAggregate.scala:134)
	at org.apache.flink.table.api.BatchTableEnvironment.translate(BatchTableEnvironment.scala:305)
	at org.apache.flink.table.api.BatchTableEnvironment.translate(BatchTableEnvironment.scala:289)
	at org.apache.flink.table.api.java.BatchTableEnvironment.toDataSet(BatchTableEnvironment.scala:146)

{code}



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