HHH-19389 proper error when @Struct is used on Dialect with no support for UDTs

hibernate-core/src/main/java/org/hibernate/boot/model/internal/AggregateComponentSecondPass.java

@@ -90,7 +90,11 @@ public void doSecondPass(Map<String, PersistentClass> persistentClasses) throws
 					structName.getCatalogName(),
 					structName.getSchemaName()
 			);
-			final UserDefinedObjectType udt = new UserDefinedObjectType( "orm", namespace, structName.getObjectName() );
+			if ( !database.getDialect().supportsUserDefinedTypes() ) {
+				throw new MappingException( "Database does not support user-defined types (remove '@Struct' annotation)" );
+			}
+			final UserDefinedObjectType udt =
+					new UserDefinedObjectType( "orm", namespace, structName.getObjectName() );
 			final Comment comment = componentClassDetails.getDirectAnnotationUsage( Comment.class );
 			if ( comment != null ) {
 				udt.setComment( comment.value() );
@@ -231,17 +235,15 @@ else if ( value instanceof Collection collection ) {
 	}
 
 	private boolean isAggregateArray() {
-		switch ( component.getAggregateColumn().getSqlTypeCode( context.getMetadataCollector() ) ) {
-			case SqlTypes.STRUCT_ARRAY:
-			case SqlTypes.STRUCT_TABLE:
-			case SqlTypes.JSON_ARRAY:
-			case SqlTypes.XML_ARRAY:
-			case SqlTypes.ARRAY:
-			case SqlTypes.TABLE:
-				return true;
-			default:
-				return false;
-		}
+		return switch ( component.getAggregateColumn().getSqlTypeCode( context.getMetadataCollector() ) ) {
+			case SqlTypes.STRUCT_ARRAY,
+				SqlTypes.STRUCT_TABLE,
+				SqlTypes.JSON_ARRAY,
+				SqlTypes.XML_ARRAY,
+				SqlTypes.ARRAY,
+				SqlTypes.TABLE -> true;
+			default -> false;
+		};
 	}
 
 	private void orderColumns(UserDefinedObjectType userDefinedType, int[] originalOrder) {

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

@@ -268,6 +268,11 @@ public int getDefaultDecimalPrecision() {
 		return 31;
 	}
 
+	@Override
+	public boolean supportsUserDefinedTypes() {
+		return true;
+	}
+
 	@Override
 	protected boolean supportsPredicateAsExpression() {
 		return getDB2Version().isSameOrAfter( 11 );

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

@@ -4506,6 +4506,17 @@ public AggregateSupport getAggregateSupport() {
 		return AggregateSupportImpl.INSTANCE;
 	}
 
+	/**
+	 * Does the database support user defined types?
+	 *
+	 * @see org.hibernate.annotations.Struct
+	 *
+	 * @since 7.1
+	 */
+	public boolean supportsUserDefinedTypes() {
+		return false;
+	}
+
 	/**
 	 * Does this database have native support for ANSI SQL standard arrays which
 	 * are expressed in terms of the element type name: {@code integer array}.

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

@@ -953,6 +953,11 @@ public boolean supportsBitType() {
 		return false;
 	}
 
+	@Override
+	public boolean supportsUserDefinedTypes() {
+		return true;
+	}
+
 	@Override
 	public String getArrayTypeName(String javaElementTypeName, String elementTypeName, Integer maxLength) {
 		return ( javaElementTypeName == null ? elementTypeName : javaElementTypeName ) + "Array";

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

@@ -1132,6 +1132,11 @@ public int getMaxIdentifierLength() {
 		return 63;
 	}
 
+	@Override
+	public boolean supportsUserDefinedTypes() {
+		return true;
+	}
+
 	@Override
 	public boolean supportsStandardArrays() {
 		return true;