Retrieve single column of type byte array fails

[MikePryadko]

Expected Behavior

Success retrieve one column of type byte[]

Actual Behaviour

Micronaut tries map array to single byte and throws exception

Steps To Reproduce

1. Use Micronaut 4.10.9
2. Create table:

CREATE TABLE customers (
    id BIGINT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
    dek BYTEA NOT NULL
);

3. Create entity:

@MappedEntity("customers")
public record CustomerEntity(
        @Id
        @GeneratedValue
        Long id,
        byte[] dek
) {}

4. Create repository

@JdbcRepository(dialect = Dialect.POSTGRES)
public interface CustomerRepository extends CrudRepository<CustomerEntity, Long> {
    @Query("SELECT dek FROM customers WHERE id = :id")
    Optional<byte[]> findDekById(long id);
}

5. Try to use and get error:

Caused by: io.micronaut.data.exceptions.DataAccessException: Cannot convert type [class [B] with value [[B@4d23b0d7] to target type: class java.lang.Byte. Consider defining a TypeConverter bean to handle this case.
	at io.micronaut.data.runtime.mapper.ResultReader.lambda$convertRequired$0(ResultReader.java:51)
	at java.base/java.util.Optional.orElseThrow(Optional.java:403)
	at io.micronaut.data.runtime.mapper.ResultReader.convertRequired(ResultReader.java:50)
	at io.micronaut.data.runtime.operations.internal.sql.AbstractSqlRepositoryOperations$4.map(AbstractSqlRepositoryOperations.java:810)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.findOne(DefaultJdbcRepositoryOperations.java:380)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.lambda$findOne$0(DefaultJdbcRepositoryOperations.java:354)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.lambda$executeRead$23(DefaultJdbcRepositoryOperations.java:820)
	at io.micronaut.data.connection.support.AbstractConnectionOperations.executeWithNewConnection(AbstractConnectionOperations.java:174)

6. Change methods return type:

    @Query("SELECT dek FROM customers WHERE id = :id")
    byte[] findDekById(long id);

7. Try to use and get another error:

Caused by: io.micronaut.data.exceptions.DataAccessException: Error executing SQL Query: SELECT dek FROM customers WHERE id = ? Error reading object for index [1] from result set: Bad value for type byte : \x0b215bc7ee274afebb1997414b5687ec09835ebe67905876acd8e67d9ae97b64
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.findAll(DefaultJdbcRepositoryOperations.java:403)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.lambda$findAll$5(DefaultJdbcRepositoryOperations.java:558)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.lambda$executeRead$23(DefaultJdbcRepositoryOperations.java:820)
	at io.micronaut.data.connection.support.AbstractConnectionOperations.executeWithNewConnection(AbstractConnectionOperations.java:174)
	at io.micronaut.data.connection.support.AbstractConnectionOperations.execute(AbstractConnectionOperations.java:114)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.executeRead(DefaultJdbcRepositoryOperations.java:817)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.findAll(DefaultJdbcRepositoryOperations.java:558)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.findAll(DefaultJdbcRepositoryOperations.java:145)

Environment Information

• Ubuntu 24.04.1
• openjdk 21.0.10 2026-01-20
• PostgreSQL 18.3

Example Application

No response

Version

4.10.9

[MikePryadko]

Try to use interface projection:

public interface DekProjection {
    byte[] getDek();
}

    @Query("SELECT dek FROM customers WHERE id = :id")
    DekProjection findDekById(long id);

Got error:

Caused by: io.micronaut.data.exceptions.DataAccessException: Cannot convert type [class [B] with value [[B@631b784] to target type: interface test.project.entity.DekProjection. Consider defining a TypeConverter bean to handle this case.
	at io.micronaut.data.runtime.mapper.ResultReader.lambda$convertRequired$0(ResultReader.java:51)
	at java.base/java.util.Optional.orElseThrow(Optional.java:403)
	at io.micronaut.data.runtime.mapper.ResultReader.convertRequired(ResultReader.java:50)
	at io.micronaut.data.runtime.operations.internal.sql.AbstractSqlRepositoryOperations$4.map(AbstractSqlRepositoryOperations.java:810)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.findOne(DefaultJdbcRepositoryOperations.java:380)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.lambda$findOne$0(DefaultJdbcRepositoryOperations.java:354)
	at io.micronaut.data.jdbc.operations.DefaultJdbcRepositoryOperations.lambda$executeRead$23(DefaultJdbcRepositoryOperations.java:820)
	at io.micronaut.data.connection.support.AbstractConnectionOperations.executeWithNewConnection(AbstractConnectionOperations.java:174)

[MikePryadko]

Ugly, but working solution:

// special model
@MappedEntity
public record OnlyDek(byte[] dek) {}

// in repo
@Query("SELECT dek FROM customers WHERE id = :id")
OnlyDek findDekById(long id);

[radovanradic]

This appears to be fixed for Optional<byte[]> in 5.0 that will be released in April/May. Until then I guess you can use your DTO workaround, just does not have to be @MappedEntity, can be something like this

@Introspected
public record OnlyDek(byte[] dek) {}