make the relations produced by the dedup SparkPropagateRelation jon unique

dhp-workflows/dhp-dedup-openaire/src/main/java/eu/dnetlib/dhp/oa/dedup/SparkPropagateRelation.java

@@ -7,6 +7,7 @@ import org.apache.commons.io.IOUtils;
 import org.apache.spark.SparkConf;
 import org.apache.spark.api.java.function.MapFunction;
 import org.apache.spark.sql.*;
+import org.apache.spark.sql.expressions.Aggregator;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -95,7 +96,49 @@ public class SparkPropagateRelation extends AbstractSparkAction {
 			FieldType.TARGET,
 			getDeletedFn());
 
-		save(newRels.union(updated).union(mergeRels), outputRelationPath, SaveMode.Overwrite);
+		save(distinctRelations(newRels.union(updated).union(mergeRels)), outputRelationPath, SaveMode.Overwrite);
+	}
+
+	private Dataset<Relation> distinctRelations(Dataset<Relation> rels) {
+		return rels
+				.groupByKey((MapFunction<Relation, String>) r -> ModelSupport.idFn().apply(r), Encoders.STRING())
+				.agg(new RelationAggregator().toColumn())
+				.map((MapFunction<Tuple2<String, Relation>, Relation>) t -> t._2(), Encoders.bean(Relation.class));
+	}
+
+	class RelationAggregator extends Aggregator<Relation, Relation, Relation> {
+
+		@Override
+		public Relation zero() {
+			return new Relation();
+		}
+
+		@Override
+		public Relation reduce(Relation b, Relation a) {
+			b.mergeFrom(a);
+			return b;
+		}
+
+		@Override
+		public Relation merge(Relation b, Relation a) {
+			b.mergeFrom(a);
+			return b;
+		}
+
+		@Override
+		public Relation finish(Relation r) {
+			return r;
+		}
+
+		@Override
+		public Encoder<Relation> bufferEncoder() {
+			return Encoders.bean(Relation.class);
+		}
+
+		@Override
+		public Encoder<Relation> outputEncoder() {
+			return Encoders.bean(Relation.class);
+		}
 	}
 
 	private static Dataset<Relation> processDataset(