try using MERGE on Db2

Author: gavinking

hibernate-core/src/main/java/org/hibernate/dialect/DB2Dialect.java

@@ -26,6 +26,7 @@
 import org.hibernate.dialect.sequence.DB2SequenceSupport;
 import org.hibernate.dialect.sequence.SequenceSupport;
 import org.hibernate.dialect.sql.ast.DB2SqlAstTranslator;
+import org.hibernate.dialect.sql.ast.PostgreSQLSqlAstTranslator;
 import org.hibernate.dialect.type.DB2StructJdbcType;
 import org.hibernate.dialect.unique.AlterTableUniqueIndexDelegate;
 import org.hibernate.dialect.unique.UniqueDelegate;
@@ -45,6 +46,7 @@
 import org.hibernate.mapping.Table;
 import org.hibernate.metamodel.mapping.EntityMappingType;
 import org.hibernate.metamodel.spi.RuntimeModelCreationContext;
+import org.hibernate.persister.entity.mutation.EntityMutationTarget;
 import org.hibernate.procedure.internal.DB2CallableStatementSupport;
 import org.hibernate.procedure.spi.CallableStatementSupport;
 import org.hibernate.query.common.TemporalUnit;
@@ -63,6 +65,9 @@
 import org.hibernate.sql.ast.spi.StandardSqlAstTranslatorFactory;
 import org.hibernate.sql.ast.tree.Statement;
 import org.hibernate.sql.exec.spi.JdbcOperation;
+import org.hibernate.sql.model.MutationOperation;
+import org.hibernate.sql.model.internal.OptionalTableUpdate;
+import org.hibernate.sql.model.jdbc.OptionalTableUpdateOperation;
 import org.hibernate.tool.schema.extract.internal.SequenceInformationExtractorDB2DatabaseImpl;
 import org.hibernate.tool.schema.extract.internal.SequenceInformationExtractorNoOpImpl;
 import org.hibernate.tool.schema.extract.spi.SequenceInformationExtractor;
@@ -169,16 +174,20 @@ protected void applyAggregateColumnCheck(StringBuilder buf, AggregateColumn aggr
 		}
 	};
 
+	private final OptionalTableUpdateStrategy optionalTableUpdateStrategy;
+
 	public DB2Dialect() {
 		this( MINIMUM_VERSION );
 	}
 
 	public DB2Dialect(DialectResolutionInfo info) {
-		super( info );
+		this( info.makeCopyOrDefault( MINIMUM_VERSION ) );
+		registerKeywords( info );
 	}
 
 	public DB2Dialect(DatabaseVersion version) {
 		super( version );
+		optionalTableUpdateStrategy = DB2Dialect::usingMerge;
 	}
 
 	@Override
@@ -253,6 +262,39 @@ protected void registerColumnTypes(TypeContributions typeContributions, ServiceR
 		);
 	}
 
+	@FunctionalInterface
+	private interface OptionalTableUpdateStrategy {
+		MutationOperation buildMutationOperation(
+				EntityMutationTarget mutationTarget,
+				OptionalTableUpdate optionalTableUpdate,
+				SessionFactoryImplementor factory);
+	}
+
+	@Override
+	public MutationOperation createOptionalTableUpdateOperation(
+			EntityMutationTarget mutationTarget,
+			OptionalTableUpdate optionalTableUpdate,
+			SessionFactoryImplementor factory) {
+		return optionalTableUpdateStrategy.buildMutationOperation( mutationTarget, optionalTableUpdate, factory );
+	}
+
+	private static MutationOperation usingMerge(
+			EntityMutationTarget mutationTarget,
+			OptionalTableUpdate optionalTableUpdate,
+			SessionFactoryImplementor factory) {
+		final PostgreSQLSqlAstTranslator<?> translator = new PostgreSQLSqlAstTranslator<>( factory, optionalTableUpdate );
+		return translator.createMergeOperation( optionalTableUpdate );
+	}
+
+	private static MutationOperation withoutMerge(
+			EntityMutationTarget mutationTarget,
+			OptionalTableUpdate optionalTableUpdate,
+			SessionFactoryImplementor factory) {
+		return new OptionalTableUpdateOperation( mutationTarget, optionalTableUpdate, factory );
+	}
+
+
+
 	protected UniqueDelegate createUniqueDelegate() {
 		return new AlterTableUniqueIndexDelegate( this );
 	}

hibernate-core/src/main/java/org/hibernate/dialect/sql/ast/DB2SqlAstTranslator.java

@@ -19,7 +19,7 @@
 import org.hibernate.query.common.FetchClauseType;
 import org.hibernate.sql.ast.Clause;
 import org.hibernate.sql.ast.SqlAstNodeRenderingMode;
-import org.hibernate.sql.ast.spi.AbstractSqlAstTranslator;
+import org.hibernate.sql.ast.spi.SqlAstTranslatorWithMerge;
 import org.hibernate.sql.ast.spi.SqlSelection;
 import org.hibernate.sql.ast.tree.MutationStatement;
 import org.hibernate.sql.ast.tree.SqlAstNode;
@@ -60,7 +60,7 @@
  *
  * @author Christian Beikov
  */
-public class DB2SqlAstTranslator<T extends JdbcOperation> extends AbstractSqlAstTranslator<T> {
+public class DB2SqlAstTranslator<T extends JdbcOperation> extends SqlAstTranslatorWithMerge<T> {
 
 	// We have to track whether we are in a later query for applying lateral during window emulation
 	private boolean inLateral;