Fix Xpp3 reader and writer for simple type associations with multiplicity=1

Co-authored-by: slachiewicz <[email protected]>

Author: Copilot

modello-plugins/modello-plugin-xpp3/src/main/java/org/codehaus/modello/plugin/xpp3/Xpp3ReaderGenerator.java

@@ -656,12 +656,37 @@ private void processField(
             String associationName = association.getName();
 
             if (association.isOneMultiplicity()) {
-                sc.add(tagComparison);
+                // Check if the association type is a class in the model or a simple type
+                boolean inModel = isClassInModel(
+                        association.getTo(), field.getModelClass().getModel());
 
-                sc.add("{");
-                sc.addIndented(objectName + ".set" + capFieldName + "( parse" + association.getTo() + "( parser, strict"
-                        + trackingArgs + " ) );");
-                sc.add("}");
+                if (inModel) {
+                    // It's a model class, call the parse method for that class
+                    sc.add(tagComparison);
+
+                    sc.add("{");
+                    sc.addIndented(objectName + ".set" + capFieldName + "( parse" + association.getTo()
+                            + "( parser, strict" + trackingArgs + " ) );");
+                    sc.add("}");
+                } else {
+                    // It's a simple type (like String), use primitive field handling
+                    sc.add(tagComparison);
+
+                    sc.add("{");
+                    sc.indent();
+
+                    writePrimitiveField(
+                            field,
+                            association.getTo(),
+                            objectName,
+                            objectName,
+                            "\"" + field.getName() + "\"",
+                            "set" + capFieldName,
+                            sc);
+
+                    sc.unindent();
+                    sc.add("}");
+                }
             } else {
                 // MANY_MULTIPLICITY
 

modello-plugins/modello-plugin-xpp3/src/main/java/org/codehaus/modello/plugin/xpp3/Xpp3WriterGenerator.java

@@ -329,12 +329,31 @@ private void writeClass(ModelClass modelClass, JClass jClass) throws ModelloExce
                 String associationName = association.getName();
 
                 if (association.isOneMultiplicity()) {
-                    sc.add(getValueChecker(type, value, association));
+                    // Check if the association type is a class in the model or a simple type
+                    boolean inModel = isClassInModel(
+                            association.getTo(), field.getModelClass().getModel());
 
-                    sc.add("{");
-                    sc.addIndented("write" + association.getTo() + "( (" + association.getTo() + ") " + value + ", \""
-                            + fieldTagName + "\", serializer );");
-                    sc.add("}");
+                    if (inModel) {
+                        // It's a model class, call the write method for that class
+                        sc.add(getValueChecker(type, value, association));
+
+                        sc.add("{");
+                        sc.addIndented("write" + association.getTo() + "( (" + association.getTo() + ") " + value
+                                + ", \"" + fieldTagName + "\", serializer );");
+                        sc.add("}");
+                    } else {
+                        // It's a simple type (like String), write it directly as a tag
+                        sc.add(getValueChecker(type, value, association));
+
+                        sc.add("{");
+                        sc.addIndented("serializer.startTag( NAMESPACE, " + "\"" + fieldTagName + "\" ).text( "
+                                + getValue(association.getTo(), value, xmlFieldMetadata) + " ).endTag( NAMESPACE, "
+                                + "\"" + fieldTagName + "\" );");
+                        sc.indent();
+                        writeLocationTracking(sc, uncapClassName, '"' + fieldTagName + '"');
+                        sc.unindent();
+                        sc.add("}");
+                    }
                 } else {
                     // MANY_MULTIPLICITY