Code for really basic example to explain the problem, let’s say I have two tables with the next relation:

create table parent_table(
    uuid char(36) primary key,
    name varchar(50)
);

create table child_table(
    parent_table_uuid char(36) primary key,
    name varchar(50),
    FOREIGN KEY (parent_table_uuid) REFERENCES parent_table(uuid)
);

Then I have the next JPA Entity classes:

public class Parent {
    @Id
    @Column(name = "uuid", length = 36)
    @Type(type = "uuid-char")
    private UUID uuid;
    @Column(name = "name")
    private String name;
    @OneToOne(cascade = CascadeType.ALL)
    @PrimaryKeyJoinColumn
    private Child child;
}

public class Child {
    @Id
    @Column(name = "parent_table_uuid", length = 36)
    @Type(type = "uuid-char")
    private UUID uuid;
    @Column(name = "name")
    private String name;
}

And what I try to do is:

    @Test
    void createAndPersistParentWithChild() {
        UUID parentUuid = UUID.randomUUID();
        Parent parent = Parent.builder().uuid(parentUuid).name("parent").build();
        parent.setChild(Child.builder().uuid(parentUuid).name("child").build());
        Parent saved = parentRepository.save(parent);
        assertThat(saved.getChild()).isNotNull();
    }

My expectation is that both objects will be persisted at once, and a parent object will be persisted first. But what I get is an exception and in the logs I can see that Hibernate generates insert query for the child table first:

Hibernate: 
    insert 
    into
        child_table
        (name, parent_table_uuid) 
    values
        (?, ?)
2024-04-26 15:45:42.509  WARN 46976 --- [Pool-1-worker-1] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL Error: 1452, SQLState: 23000
2024-04-26 15:45:42.510 ERROR 46976 --- [Pool-1-worker-1] o.h.engine.jdbc.spi.SqlExceptionHelper   : Cannot add or update a child row: a foreign key constraint fails (`test`.`child_table`, CONSTRAINT `fk_child_table_parent_table_uuid_to_parent_table_uuid` FOREIGN KEY (`parent_table_uuid`) REFERENCES `parent_table` (`uuid`))

Do I need to modify something to get it working? If I remove the constraint the code works perfectly fine, and both objects can be saved and retrieved.

Note: I don’t need the reference to the whole Parent object in the Child object.