HHH-15578 Add min/max emulation for uuid on PostgreSQL

hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/PostgreSQLLegacyDialect.java

@@ -39,6 +39,7 @@ import org.hibernate.dialect.RowLockStrategy;
 import org.hibernate.dialect.SelectItemReferenceStrategy;
 import org.hibernate.dialect.TimeZoneSupport;
 import org.hibernate.dialect.function.CommonFunctionFactory;
+import org.hibernate.dialect.function.PostgreSQLMinMaxFunction;
 import org.hibernate.dialect.identity.IdentityColumnSupport;
 import org.hibernate.dialect.identity.PostgreSQLIdentityColumnSupport;
 import org.hibernate.dialect.pagination.LimitHandler;
@@ -574,6 +575,60 @@ public class PostgreSQLLegacyDialect extends Dialect {
 			functionFactory.inverseDistributionOrderedSetAggregates();
 			functionFactory.hypotheticalOrderedSetAggregates();
 		}
+
+		if ( !supportsMinMaxOnUuid() ) {
+			queryEngine.getSqmFunctionRegistry().register( "min", new PostgreSQLMinMaxFunction( "min" ) );
+			queryEngine.getSqmFunctionRegistry().register( "max", new PostgreSQLMinMaxFunction( "max" ) );
+		}
+	}
+
+	/**
+	 * Whether PostgreSQL supports `min(uuid)`/`max(uuid)` which it doesn't by default.
+	 * Since the emulation is not very performant, this can be overridden by users which
+	 * make sure that an aggregate function for uuid exists on their database.
+	 *
+	 * The following definitions can be used for this purpose:
+	 *
+	 * <code>
+	 * create or replace function min(uuid, uuid)
+	 *     returns uuid
+	 *     immutable parallel safe
+	 *     language plpgsql as
+	 * $$
+	 * begin
+	 *     return least($1, $2);
+	 * end
+	 * $$;
+	 *
+	 * create aggregate min(uuid) (
+	 *     sfunc = min,
+	 *     stype = uuid,
+	 *     combinefunc = min,
+	 *     parallel = safe,
+	 *     sortop = operator (<)
+	 *     );
+	 *
+	 * create or replace function max(uuid, uuid)
+	 *     returns uuid
+	 *     immutable parallel safe
+	 *     language plpgsql as
+	 * $$
+	 * begin
+	 *     return greatest($1, $2);
+	 * end
+	 * $$;
+	 *
+	 * create aggregate max(uuid) (
+	 *     sfunc = max,
+	 *     stype = uuid,
+	 *     combinefunc = max,
+	 *     parallel = safe,
+	 *     sortop = operator (>)
+	 *     );
+	 * </code>
+	 */
+	protected boolean supportsMinMaxOnUuid() {
+		return false;
 	}
 
 	@Override

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

@@ -25,6 +25,7 @@ import org.hibernate.PessimisticLockException;
 import org.hibernate.QueryTimeoutException;
 import org.hibernate.boot.model.TypeContributions;
 import org.hibernate.dialect.function.CommonFunctionFactory;
+import org.hibernate.dialect.function.PostgreSQLMinMaxFunction;
 import org.hibernate.dialect.identity.IdentityColumnSupport;
 import org.hibernate.dialect.identity.PostgreSQLIdentityColumnSupport;
 import org.hibernate.dialect.pagination.LimitHandler;
@@ -556,6 +557,60 @@ public class PostgreSQLDialect extends Dialect {
 		// Note that PostgreSQL doesn't support the OVER clause for ordered set-aggregate functions
 		functionFactory.inverseDistributionOrderedSetAggregates();
 		functionFactory.hypotheticalOrderedSetAggregates();
+
+		if ( !supportsMinMaxOnUuid() ) {
+			queryEngine.getSqmFunctionRegistry().register( "min", new PostgreSQLMinMaxFunction( "min" ) );
+			queryEngine.getSqmFunctionRegistry().register( "max", new PostgreSQLMinMaxFunction( "max" ) );
+		}
+	}
+
+	/**
+	 * Whether PostgreSQL supports `min(uuid)`/`max(uuid)` which it doesn't by default.
+	 * Since the emulation is not very performant, this can be overridden by users which
+	 * make sure that an aggregate function for uuid exists on their database.
+	 *
+	 * The following definitions can be used for this purpose:
+	 *
+	 * <code>
+	 * create or replace function min(uuid, uuid)
+	 *     returns uuid
+	 *     immutable parallel safe
+	 *     language plpgsql as
+	 * $$
+	 * begin
+	 *     return least($1, $2);
+	 * end
+	 * $$;
+	 *
+	 * create aggregate min(uuid) (
+	 *     sfunc = min,
+	 *     stype = uuid,
+	 *     combinefunc = min,
+	 *     parallel = safe,
+	 *     sortop = operator (<)
+	 *     );
+	 *
+	 * create or replace function max(uuid, uuid)
+	 *     returns uuid
+	 *     immutable parallel safe
+	 *     language plpgsql as
+	 * $$
+	 * begin
+	 *     return greatest($1, $2);
+	 * end
+	 * $$;
+	 *
+	 * create aggregate max(uuid) (
+	 *     sfunc = max,
+	 *     stype = uuid,
+	 *     combinefunc = max,
+	 *     parallel = safe,
+	 *     sortop = operator (>)
+	 *     );
+	 * </code>
+	 */
+	protected boolean supportsMinMaxOnUuid() {
+		return false;
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/dialect/function/PostgreSQLMinMaxFunction.java

@@ -0,0 +1,110 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or http://www.gnu.org/licenses/lgpl-2.1.html
+ */
+package org.hibernate.dialect.function;
+
+import java.util.List;
+
+import org.hibernate.metamodel.mapping.JdbcMapping;
+import org.hibernate.query.sqm.function.AbstractSqmSelfRenderingFunctionDescriptor;
+import org.hibernate.query.sqm.function.FunctionKind;
+import org.hibernate.query.sqm.produce.function.ArgumentTypesValidator;
+import org.hibernate.query.sqm.produce.function.StandardArgumentsValidators;
+import org.hibernate.query.sqm.produce.function.StandardFunctionArgumentTypeResolvers;
+import org.hibernate.query.sqm.produce.function.StandardFunctionReturnTypeResolvers;
+import org.hibernate.sql.ast.Clause;
+import org.hibernate.sql.ast.SqlAstTranslator;
+import org.hibernate.sql.ast.spi.SqlAppender;
+import org.hibernate.sql.ast.tree.SqlAstNode;
+import org.hibernate.sql.ast.tree.expression.Expression;
+import org.hibernate.sql.ast.tree.predicate.Predicate;
+import org.hibernate.type.SqlTypes;
+
+import static org.hibernate.query.sqm.produce.function.FunctionParameterType.COMPARABLE;
+
+/**
+ * PostgreSQL doesn't support min/max for uuid yet,
+ * but since that type is comparable we want to support this operation.
+ * The workaround is to cast uuid to text and aggregate that, which preserves the ordering,
+ * and finally cast the result back to uuid.
+ *
+ * @author Christian Beikov
+ */
+public class PostgreSQLMinMaxFunction extends AbstractSqmSelfRenderingFunctionDescriptor {
+
+	public PostgreSQLMinMaxFunction(String name) {
+		super(
+				name,
+				FunctionKind.AGGREGATE,
+				new ArgumentTypesValidator( StandardArgumentsValidators.exactly( 1 ), COMPARABLE ),
+				StandardFunctionReturnTypeResolvers.useFirstNonNull(),
+				StandardFunctionArgumentTypeResolvers.IMPLIED_RESULT_TYPE
+		);
+	}
+
+	@Override
+	public void render(SqlAppender sqlAppender, List<? extends SqlAstNode> sqlAstArguments, SqlAstTranslator<?> walker) {
+		render( sqlAppender, sqlAstArguments, null, walker );
+	}
+
+	@Override
+	public void render(
+			SqlAppender sqlAppender,
+			List<? extends SqlAstNode> sqlAstArguments,
+			Predicate filter,
+			SqlAstTranslator<?> translator) {
+		final boolean caseWrapper = filter != null && !translator.supportsFilterClause();
+		sqlAppender.appendSql( getName() );
+		sqlAppender.appendSql( '(' );
+		final Expression arg = (Expression) sqlAstArguments.get( 0 );
+		final String castTarget;
+		if ( caseWrapper ) {
+			translator.getCurrentClauseStack().push( Clause.WHERE );
+			sqlAppender.appendSql( "case when " );
+			filter.accept( translator );
+			translator.getCurrentClauseStack().pop();
+			sqlAppender.appendSql( " then " );
+			castTarget = renderArgument( sqlAppender, translator, arg );
+			sqlAppender.appendSql( " else null end)" );
+		}
+		else {
+			castTarget = renderArgument( sqlAppender, translator, arg );
+			sqlAppender.appendSql( ')' );
+			if ( filter != null ) {
+				translator.getCurrentClauseStack().push( Clause.WHERE );
+				sqlAppender.appendSql( " filter (where " );
+				filter.accept( translator );
+				sqlAppender.appendSql( ')' );
+				translator.getCurrentClauseStack().pop();
+			}
+		}
+		if ( castTarget != null ) {
+			sqlAppender.appendSql( "::" );
+			sqlAppender.appendSql( castTarget );
+		}
+	}
+
+	private String renderArgument(SqlAppender sqlAppender, SqlAstTranslator<?> translator, Expression arg) {
+		final JdbcMapping sourceMapping = arg.getExpressionType().getJdbcMappings().get( 0 );
+		// Cast uuid expressions to "text" first, aggregate that, and finally cast to uuid again
+		if ( sourceMapping.getJdbcType().getDefaultSqlTypeCode() == SqlTypes.UUID ) {
+			sqlAppender.appendSql( "cast(" );
+			arg.accept( translator );
+			sqlAppender.appendSql( " as text)" );
+			return "uuid";
+		}
+		else {
+			arg.accept( translator );
+			return null;
+		}
+	}
+
+	@Override
+	public String getArgumentListSignature() {
+		return "(COMPARABLE arg)";
+	}
+
+}