hibernate/hibernate-orm · error · UnsupportedOperationException

Support for attribute mapping type not yet implemented:

Error message

Support for attribute mapping type not yet implemented: 

What it means

XmlHelper.toString serializes XML aggregates but implements only two attribute mapping kinds: basic selectables and nested embeddables (EmbeddedAttributeMapping). When writing, any other attribute kind inside the embeddable - a to-one association, a discriminated (@Any) association, or a plural/collection attribute - throws UnsupportedOperationException with the mapping class name.

Source

Thrown at hibernate-core/src/main/java/org/hibernate/type/descriptor/jdbc/XmlHelper.java:810

						sb.append( "/>" );
						continue;
					}
					sb.append( '>' );
				}
				toString(
						mappingType,
						attributeValue == null ? null : mappingType.getValues( attributeValue ),
						options,
						sb
				);
				if ( tagName != null ) {
					sb.append( "</" );
					sb.append( tagName );
					sb.append( '>' );
				}
			}
			else {
				throw new UnsupportedOperationException( "Support for attribute mapping type not yet implemented: " + attributeMapping.getClass().getName() );
			}
		}
	}

	private static void convertedBasicValueToString(
			XMLAppender appender,
			Object value,
			WrapperOptions options,
			JavaType<Object> jdbcJavaType,
			JdbcType jdbcType) {
		switch ( jdbcType.getDefaultSqlTypeCode() ) {
			case SqlTypes.TINYINT:
			case SqlTypes.SMALLINT:
			case SqlTypes.INTEGER:
				if ( value instanceof Boolean booleanValue ) {
					// BooleanJavaType has this as an implicit conversion
					appender.append( booleanValue ? '1' : '0' );
					break;

View on GitHub (pinned to fad1729dce)

Solutions

1. Restrict XML-mapped embeddables to basic fields and nested embeddables only.
2. Replace the association with plain FK columns stored as basic attributes inside the aggregate.
3. Move associations and collections out of the aggregate onto the owning entity.
4. Check the Hibernate version's aggregate support matrix before adding such attributes.

Example fix

// before
@Embeddable
public class Contact {
    String email;
    @OneToMany(mappedBy = "contact")   // collection inside XML aggregate
    List<Phone> phones;                // -> Support for attribute mapping type not yet implemented
}
// after: keep only scalars in the aggregate
@Embeddable
public class Contact {
    String email;
    String primaryPhone;
}

static void assertXmlAggregateWritable(Class<?> embeddable) {
    for (Field f : embeddable.getDeclaredFields()) {
        if (f.isAnnotationPresent(ManyToOne.class) || f.isAnnotationPresent(OneToOne.class)
                || f.isAnnotationPresent(OneToMany.class) || f.isAnnotationPresent(ManyToMany.class)
                || f.isAnnotationPresent(Any.class)) {
            throw new IllegalStateException(
                "XML aggregate cannot serialize attribute: " + f);
        }
    }
}

try {
    session.persist(person);   // or merge/update
} catch (UnsupportedOperationException ex) {
    if (ex.getMessage() != null && ex.getMessage().startsWith("Support for attribute mapping type")) {
        throw new DataMappingException("XML aggregate contains unsupported attribute type", ex);
    }
    throw ex;
}

When it happens

Trigger: Inserting or updating an entity whose XML-mapped embeddable contains a @ManyToOne/@OneToOne, @Any, or collection attribute. The failure occurs at write time when the aggregate is serialized to the XML column.

Common situations: Growing an existing XML aggregate embeddable with an association during development; porting struct mappings (which allow to-one FK parts) to XML columns; upgrades that surface previously latent mappings.

Related errors

• Illegal XML content:
• XML not properly formatted:
• XML not properly formed:
• XML starts sub-object for a non-aggregate type at index %d.
• Unsupported JdbcType nested in struct:

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/d99a2b9124ccaccd. Report an issue: GitHub.