From d1119d320a96695341d102480648752a7208525b Mon Sep 17 00:00:00 2001
From: Gavin King <gavin@hibernate.org>
Date: Sun, 23 Aug 2020 10:33:56 +0200
Subject: [PATCH] HHH-14153 optimize away temp table for single-table HQL
 update

When a HQL bulk update query only touches a single table,
use BasicExecutor instead of MultiTableUpdateExecutor.

This is an alternate implementation to the one proposed by
@NathanQingyangXu in #3508 and loosely based on that work.
---
 .../org/hibernate/hql/internal/ast/HqlSqlWalker.java |  4 ++--
 .../hql/internal/ast/QueryTranslatorImpl.java        | 10 ++++++----
 .../hql/internal/ast/exec/BasicExecutor.java         | 12 +++++++++++-
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/HqlSqlWalker.java b/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/HqlSqlWalker.java
index c6db01e8ad..bdb8ced180 100644
--- a/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/HqlSqlWalker.java
+++ b/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/HqlSqlWalker.java
@@ -141,7 +141,7 @@ public class HqlSqlWalker extends HqlSqlBaseWalker implements ErrorReporter, Par
 	private ArrayList<ParameterSpecification> parameterSpecs = new ArrayList<>();
 	private int numberOfParametersInSetClause;
 
-	private ArrayList assignmentSpecifications = new ArrayList();
+	private ArrayList<AssignmentSpecification> assignmentSpecifications = new ArrayList<>();
 
 	private JoinType impliedJoinType = JoinType.INNER_JOIN;
 
@@ -1393,7 +1393,7 @@ public class HqlSqlWalker extends HqlSqlBaseWalker implements ErrorReporter, Par
 		}
 	}
 
-	public ArrayList getAssignmentSpecifications() {
+	public ArrayList<AssignmentSpecification> getAssignmentSpecifications() {
 		return assignmentSpecifications;
 	}
 
diff --git a/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/QueryTranslatorImpl.java b/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/QueryTranslatorImpl.java
index 21d94d1e64..e2efb5ad4d 100644
--- a/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/QueryTranslatorImpl.java
+++ b/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/QueryTranslatorImpl.java
@@ -63,6 +63,8 @@ import antlr.RecognitionException;
 import antlr.TokenStreamException;
 import antlr.collections.AST;
 
+import static java.util.Collections.singleton;
+
 /**
  * A QueryTranslator that uses an Antlr-based parser.
  *
@@ -609,10 +611,10 @@ public class QueryTranslatorImpl implements FilterTranslator {
 		else if ( walker.getStatementType() == HqlSqlTokenTypes.UPDATE ) {
 			final FromElement fromElement = walker.getFinalFromClause().getFromElement();
 			final Queryable persister = fromElement.getQueryable();
-			if ( persister.isMultiTable() ) {
-				// even here, if only properties mapped to the "base table" are referenced
-				// in the set and where clauses, this could be handled by the BasicDelegate.
-				// TODO : decide if it is better performance-wise to doAfterTransactionCompletion that check, or to simply use the MultiTableUpdateDelegate
+
+			boolean affectsExtraTables = persister.isMultiTable()
+					&& !singleton( persister.getTableName() ).containsAll( walker.getQuerySpaces() );
+			if ( affectsExtraTables ) {
 				return new MultiTableUpdateExecutor( walker );
 			}
 			else {
diff --git a/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/exec/BasicExecutor.java b/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/exec/BasicExecutor.java
index e000e39ec7..f178b9e61c 100644
--- a/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/exec/BasicExecutor.java
+++ b/hibernate-core/src/main/java/org/hibernate/hql/internal/ast/exec/BasicExecutor.java
@@ -17,6 +17,7 @@ import org.hibernate.engine.spi.QueryParameters;
 import org.hibernate.engine.spi.RowSelection;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.event.spi.EventSource;
+import org.hibernate.hql.internal.antlr.HqlSqlTokenTypes;
 import org.hibernate.hql.internal.ast.HqlSqlWalker;
 import org.hibernate.hql.internal.ast.QuerySyntaxException;
 import org.hibernate.hql.internal.ast.SqlGenerator;
@@ -40,7 +41,16 @@ public class BasicExecutor implements StatementExecutor {
 		try {
 			SqlGenerator gen = new SqlGenerator( walker.getSessionFactoryHelper().getFactory() );
 			gen.statement( walker.getAST() );
-			sql = gen.getSQL();
+			if ( walker.getStatementType() == HqlSqlTokenTypes.UPDATE ) {
+				// workaround for a problem where HqlSqlWalker actually generates
+				// broken SQL with undefined aliases in the where clause, because
+				// that is what MultiTableUpdateExecutor is expecting to get
+				String alias = walker.getFinalFromClause().getFromElement().getTableAlias();
+				sql = gen.getSQL().replace( alias + ".", "" );
+			}
+			else {
+				sql = gen.getSQL();
+			}
 			gen.getParseErrorHandler().throwQueryException();
 			parameterSpecifications = gen.getCollectedParameters();
 		}