hibernate/hibernate-orm · error · InstantiationException

Cannot instantiate query result type

Error message

Cannot instantiate query result type

What it means

Thrown from RowTransformerConstructorImpl.transformRow: a matching constructor was found, but invoking it via reflection on a result row threw. The original exception (e.g. NullPointerException from inside the DTO constructor, IllegalArgumentException from a null passed to a primitive parameter, IllegalAccessException under JPMS restrictions) is attached as the cause - always read `getCause()`. Unlike 3187/3188 this happens per-row at execution time, so the query plan built fine and some or all rows fail.

Source

Thrown at hibernate-core/src/main/java/org/hibernate/sql/results/internal/RowTransformerConstructorImpl.java:68

	private static Class<?> resolveElementJavaType(TupleElement<?> element) {
		if ( element instanceof SqmExpressibleAccessor<?> accessor ) {
			final SqmExpressible<?> expressible = accessor.getExpressible();
			if ( expressible != null && expressible.getExpressibleJavaType() != null ) {
				return expressible.getExpressibleJavaType().getJavaTypeClass();
			}
		}

		return element.getJavaType();
	}

	@Override
	public T transformRow(Object[] row) {
		try {
			return constructor.newInstance( row );
		}
		catch (Exception e) {
			throw new InstantiationException( "Cannot instantiate query result type", type, e );
		}
	}

	@Override
	public int determineNumberOfResultElements(int rawElementCount) {
		return 1;
	}
}

View on GitHub (pinned to fad1729dce)

Solutions

1. Inspect the wrapped cause (`e.getCause()`) - it names the real failure inside the constructor
2. Make constructor parameters nullable-safe: use wrapper types instead of primitives, handle nulls explicitly
3. Open the DTO package for reflection (`--add-opens java.base/...` or `opens` in module-info) or make the class and constructor public
4. Fix or filter the offending data (e.g. `where e.closedOn is not null`)

Example fix

// before
public ReportDto(String title, int pages) { this.title = Objects.requireNonNull(title); }
// after
public ReportDto(String title, Integer pages) { this.title = title; this.pages = pages == null ? 0 : pages; }

// Before mapping rows, null-check nullable columns your constructor rejects
if (row[0] == null) { /* substitute default or skip row */ }

try { dto = query.getSingleResult(); }
catch (org.hibernate.InstantiationException e) {
    Throwable real = e.getCause(); // the exception thrown inside the constructor
    // handle NPE/IAE from bad data, or reflective access failures
}

When it happens

Trigger: DTO constructor that throws on unexpected values (nulls, empty strings, invalid enum text parsed inside the constructor); a null database value passed to a primitive constructor parameter; constructor made non-public or module not opened so reflective access fails; data-driven failures that only occur for specific rows (bad enum name, null column).

Common situations: Defensive DTO constructors with Objects.requireNonNull on nullable columns; upgrading to JDK 16+ where reflective access to non-public classes is denied unless the package is opened; new rows with nulls in columns that were previously NOT NULL.

Related errors

• Unable to generate set of all hints - {}
• Could not instantiate entity
• Could not instantiate managed bean directly
• Error performing the dynamic instantiation
• Error instantiating class '{}' using default constructor: {}

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/dc188fa6720fc3dc. Report an issue: GitHub.