hibernate/hibernate-orm · error · UnsupportedOperationException

Support for model part type not yet implemented:

Error message

Support for model part type not yet implemented: 

What it means

While flattening an embeddable into JSON, serializeObjectValues walks each sub-part (getSubPart) and hands it to serializeModelPart. Only two model-part shapes are serializable: SelectableMapping (plain column-backed values, written as key + visit) and EmbeddedAttributeMapping (nested embeddables). Anything else - to-one associations, plural attributes, @Any mappings, custom ValuedModelPart implementations - has no JSON key/value form, so Hibernate throws UnsupportedOperationException with the model part class name, or 'null' when the part itself is null.

Source

Thrown at hibernate-core/src/main/java/org/hibernate/type/descriptor/jdbc/spi/JsonGeneratingVisitor.java:269

			visit( modelPart.getMappedType(), value, options, writer );
		}
		else if ( modelPart instanceof EmbeddedAttributeMapping embeddedAttribute ) {
			if ( value != null ) {
				final EmbeddableMappingType mappingType = embeddedAttribute.getMappedType();
				final SelectableMapping aggregateMapping = mappingType.getAggregateMapping();
				if ( aggregateMapping == null ) {
					serializeObjectValues( mappingType, value, options, writer );
				}
				else {
					final String name = aggregateMapping.getSelectableName();
					writer.objectKey( name );
					visit( mappingType, value, options, writer );
				}
			}
		}
		else {
			// could not handle model part, throw exception
			throw new UnsupportedOperationException(
					"Support for model part type not yet implemented: "
					+ (modelPart != null ? modelPart.getClass().getName() : "null")
			);
		}
	}

	protected void serializeEntity(
			Object value,
			EntityMappingType entityType,
			WrapperOptions options,
			JsonDocumentWriter writer) throws IOException {
		// We only need the identifier here
		final EntityIdentifierMapping identifierMapping = entityType.getIdentifierMapping();
		serializeEntityIdentifier( value, identifierMapping, options, writer );
	}

	protected void serializeEntityIdentifier(
			Object value,

View on GitHub (pinned to fad1729dce)

Solutions

1. Remove the association field from the JSON-mapped embeddable or annotate it @Transient
2. Replace the association inside the embeddable with a plain FK column (e.g. Long otherId), which is a basic SelectableMapping and serializes fine
3. Keep associations on the owning entity instead of inside the aggregate
4. Upgrade Hibernate ORM in case additional model parts became serializable

Example fix

// before
@Embeddable
class Address {
    @ManyToOne
    private Country country; // association inside JSON aggregate -> 'Support for model part type not yet implemented'
}

// after
@Embeddable
class Address {
    @Column(name = "country_id")
    private Long countryId; // basic FK column serializes as a JSON value
}

// Fail fast at startup: scan embeddables used in JSON aggregates for association fields
for (Field f : embeddableClass.getDeclaredFields()) {
    if (f.isAnnotationPresent(ManyToOne.class) || f.isAnnotationPresent(OneToOne.class)
            || f.isAnnotationPresent(Any.class) || f.isAnnotationPresent(OneToMany.class)
            || f.isAnnotationPresent(ManyToMany.class)) {
        if (!f.isAnnotationPresent(Transient.class)) {
            throw new IllegalStateException("Association inside JSON-mapped embeddable: " + f);
        }
    }
}

When it happens

Trigger: An @Embeddable stored as a JSON aggregate (e.g. @JdbcTypeCode(SqlTypes.JSON) on an @Embedded attribute for PostgreSQL jsonb / Oracle JSON) that declares @ManyToOne, @OneToOne, @Any or a collection field; during flush or query-result writing the association's model part (e.g. ToOneAttributeMapping) reaches serializeModelPart and is rejected.

Common situations: Reusing domain embeddables originally written for plain relational mapping inside JSON columns; retrofitting JSON storage onto an existing model that keeps entity references inside value objects.

Related errors

• Could not find selectable [%s] in embeddable type [%s] for J
• Can't parse JSON object for selectable [%s] which is not of
• Failed to serialize JSON mapping
• Unsupported foreign key part:
• Unwrap strategy not known for this Java type: " + getTypeNam

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/5ae22b35bce18870. Report an issue: GitHub.