[BUG] `DataJpaTest` failed with a H2 Constraint when inserting a Entity with a boolean property annotated with @Convert(converter = YesNoConverter.class)

[xtermi2]

All my @DataJpaTest tests fail when I try to insert / update a @Entity when the @Entity has a Boolean property annotated with a @Converter (like org.hibernate.type.YesNoConverter, but also with a similar Converter implemented by us)

• Affected environments: Spring Boot 4.0.2 and 4.1.0-M1
• Works correctly on Spring Boot 3.5.10
• Demo Project (created with the spring initializr) to reproduce the issue: https://github.com/xtermi2/data-jpa-test-with-boolean-converter-issue
• Inserting null values works as expected

The JPA Entity

@Entity
public class MyEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long id;

    @Version
    private Integer version;

    @Convert(converter = YesNoConverter.class)
    private Boolean paused;

    @Column(length = 120)
    private String name;
...

The Test

@DataJpaTest(showSql = true, properties = {
        "spring.jpa.show-sql=true",
        "spring.jpa.properties.hibernate.format_sql=true",
        "logging.level.org.hibernate.SQL=DEBUG",
        "logging.level.org.hibernate.orm.jdbc.bind=TRACE",
})
class MyEntityRepositoryTest {

    @Autowired
    private MyEntityRepository repository;

    @Autowired
    private EntityManager entityManager;

    @Test
    void testWithConverter() {
        MyEntity entity = new MyEntity();
        entity.setName("Test Entity");
        entity.setPaused(true);

        MyEntity savedEntity = repository.save(entity);

        flushAndClear();

        assertThat(savedEntity.getPaused())
                .isTrue();

        savedEntity.setPaused(null);

        repository.save(savedEntity);

        flushAndClear();

        MyEntity fetchedEntity = repository.findById(savedEntity.getId()).orElseThrow();

        assertThat(fetchedEntity.getPaused())
                .isNull();
    }

    private void flushAndClear() {
        entityManager.flush();
        entityManager.clear();
    }
}

Failure Message:

Ungültige Bedingung: "CONSTRAINT_D: "
Check constraint invalid: "CONSTRAINT_D: "; SQL statement:
insert into my_entity (name,paused,version,id) values (?,?,?,?) [23514-240]

could not execute statement [Ungültige Bedingung: "CONSTRAINT_D: "
Check constraint invalid: "CONSTRAINT_D: "; SQL statement:
insert into my_entity (name,paused,version,id) values (?,?,?,?) [23514-240]] [insert into my_entity (name,paused,version,id) values (?,?,?,?)]
org.hibernate.exception.ConstraintViolationException: could not execute statement [Ungültige Bedingung: "CONSTRAINT_D: "
Check constraint invalid: "CONSTRAINT_D: "; SQL statement:
insert into my_entity (name,paused,version,id) values (?,?,?,?) [23514-240]] [insert into my_entity (name,paused,version,id) values (?,?,?,?)]

The error occured when the flush forces JPA to execute the insert in the in-memory H2 DB.
I enabled logging an can see, that the table was created correctly and the query with the parameters looking OK:

    create table my_entity (
        paused char(1) check ((paused in ('N','Y'))),
        version integer,
        id bigint not null,
        name varchar(120),
        primary key (id)
    )

insert 
    into
        my_entity
        (name, paused, version, id) 
    values
        (?, ?, ?, ?)

2026-01-29T11:27:29.819+01:00 TRACE 240391 --- [data-jpa-test-with-boolean-converter] [    Test worker] org.hibernate.orm.jdbc.bind              : binding parameter (1:VARCHAR) <- [Test Entity]
2026-01-29T11:27:29.819+01:00 TRACE 240391 --- [data-jpa-test-with-boolean-converter] [    Test worker] org.hibernate.orm.jdbc.bind              : binding parameter (2:CHAR) <- [Y]
2026-01-29T11:27:29.819+01:00 TRACE 240391 --- [data-jpa-test-with-boolean-converter] [    Test worker] org.hibernate.orm.jdbc.bind              : binding parameter (3:INTEGER) <- [0]
2026-01-29T11:27:29.819+01:00 TRACE 240391 --- [data-jpa-test-with-boolean-converter] [    Test worker] org.hibernate.orm.jdbc.bind              : binding parameter (4:BIGINT) <- [1]
2026-01-29T11:27:29.822+01:00  WARN 240391 --- [data-jpa-test-with-boolean-converter] [    Test worker] org.hibernate.orm.jdbc.error             : HHH000247: ErrorCode: 23514, SQLState: 23514
2026-01-29T11:27:29.822+01:00  WARN 240391 --- [data-jpa-test-with-boolean-converter] [    Test worker] org.hibernate.orm.jdbc.error             : Ungültige Bedingung: "CONSTRAINT_D: "

The only difference I saw that in Spring Boot 3.5 the create table statement for the affected field was paused char(1) check (paused in ('N','Y')), and with Spring Boot 4 paused char(1) check ((paused in ('N','Y'))), <- So spring Boot 4 is generating unnecessary braces.

== Workarounds
Adding @AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE) to each @DataJpaTest annotated test resolves the issue:

• the logs show the same create table statement
• the logs show the same insert statement with the same parameters

[quaff]

It's not related to Spring Data JPA, I think it's a bug of H2.

Hibernate generated legal DDL:

    create table my_entity (
        paused char(1) check ((paused in ('N','Y'))),
        version integer,
        id bigint not null,
        name varchar(120),
        primary key (id)
    )

but test against pure JDBC failed with same error:

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.jdbc.test.autoconfigure.JdbcTest;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@JdbcTest
class H2Test {

    @Autowired
    private JdbcTemplate jdbcTemplate;


    @Transactional(propagation = Propagation.NOT_SUPPORTED)
    @Test
    void test() {
        String createTable = """
                create table my_entity (
                    paused char(1) check ((paused in ('N','Y'))),
                    version integer,
                    id bigint not null,
                    name varchar(120),
                    primary key (id)
                )""";
        jdbcTemplate.execute(createTable);
        jdbcTemplate.update("insert into my_entity(name, paused, version, id) values(?, ?, ?, ?)", "Test Entity", 'Y', 0, 1);
    }
}

[xtermi2]

@quaff Yes, you are right, thanks.
Downgrading h2 to the version used in spring boot 3.5.10 worked:

ext {
    set("h2.version", "2.3.232")
}

I have open a Issue at h2: h2database/h2database#4323