hibernate/hibernate-orm · error · QueryException

Can't emulate json_objectagg 'with unique keys' clause.

Error message

Can't emulate json_objectagg 'with unique keys' clause.

What it means

Error "Can't emulate json_objectagg 'with unique keys' clause." thrown in hibernate/hibernate-orm.

Source

Thrown at hibernate-core/src/main/java/org/hibernate/dialect/function/json/MySQLJsonObjectAggFunction.java:36

/**
 * MySQL json_objectagg function.
 */
public class MySQLJsonObjectAggFunction extends JsonObjectAggFunction {

	public MySQLJsonObjectAggFunction(TypeConfiguration typeConfiguration) {
		super( ",", false, typeConfiguration );
	}

	@Override
	protected void render(
			SqlAppender sqlAppender,
			JsonObjectAggArguments arguments,
			Predicate filter,
			ReturnableType<?> returnType,
			SqlAstTranslator<?> translator) {
		final boolean caseWrapper = filter != null;
		if ( arguments.uniqueKeysBehavior() == JsonObjectAggUniqueKeysBehavior.WITH ) {
			throw new QueryException( "Can't emulate json_objectagg 'with unique keys' clause." );
		}
		sqlAppender.appendSql( "concat('{',group_concat(concat(json_quote(" );
		arguments.key().accept( translator );
		sqlAppender.appendSql( "),':'," );
		if ( caseWrapper ) {
			if ( arguments.nullBehavior() != JsonNullBehavior.ABSENT ) {
				throw new QueryException( "Can't emulate json_objectagg filter clause when using 'null on null' clause." );
			}
			translator.getCurrentClauseStack().push( Clause.WHERE );
			sqlAppender.appendSql( "case when " );
			filter.accept( translator );
			translator.getCurrentClauseStack().pop();
			sqlAppender.appendSql( " then " );
			renderArgument( sqlAppender, arguments.value(), arguments.nullBehavior(), translator );
			sqlAppender.appendSql( " else null end)" );
		}
		else {
			renderArgument( sqlAppender, arguments.value(), arguments.nullBehavior(), translator );

View on GitHub (pinned to fad1729dce)

Solutions

1. Remove the WITH UNIQUE KEYS clause.

When it happens

Trigger: Triggered when the application calls a Hibernate dialect feature that the configured database dialect cannot provide: Can't emulate json_objectagg 'with unique keys' clause (MySQL).

Common situations: Common when running against a database whose dialect lacks this capability, when a mapping or HQL/Criteria query requests unsupported functionality, or when the wrong dialect is configured for the database in use. Error: Can't emulate json_objectagg 'with unique keys' clause (MySQL).

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/28ccca6894b3da4a. Report an issue: GitHub.