It seems that I made a mistake somewhere but I can not see where.
JPA insists to generate a unique constraint on a FK of one-to-many relationship on the child side. This constraint prevents me to insert more then one record in the child table.

Parent entity:

@Entity
@Table(name = "customer")
@Data
public class CustomerDto {
    @Id
    private Long id;

    ...

    @Column(name = "notes")
    private String notes;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
    @JoinColumn(name = "customer_id")
    private List<EmailDto> emails = new ArrayList<>();

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
    @JoinColumn(name = "customer_id")
    private List<PhoneDto> phones = new ArrayList<>();
}

Child 1:

@Entity
@Table(name = "email")
@Data
public class EmailDto {
    @Id
    private Long id;

    @Column(name = "email", unique = true, length = 128)
    private String email;

    @ManyToOne(fetch = FetchType.LAZY)
    private CustomerDto customer;
}

Child 2:

@Entity
@Table(name = "phone")
@Data
public class PhoneDto {
    @Id
    private Long id;

    @Column(name = "phone_number", nullable = false, length = 32)
    private String phoneNumber;

    @OneToOne(fetch = FetchType.LAZY)
    private CustomerDto customer;
}

Tables looks as I expect:

But this also generates an extra constraint for the foreign-key on the phone side:

The email table looks ok:

The unique-contrtaint that Hibernate generates on the phone side ONLY allow me to insert ONE record per customer. If I trying to insert two phone numbers I get a duplicate key value violates unique constraint "phone_customer_id_key" error.

If I change the JoinColumn definition on the CustomerDto.java this way:

@JoinColumn(name = "customer_id") —> @JoinColumn(name = "customer_idx")

then it works and and I can save 0..* phone numbers per a customer properly.

BUT, this modification generates a stupid table structure:

What I am missing here?

I can create a proper structure with simple SQLs and I can use customer_id as a foreign keys in the child tables. But why JPA generates an extra unexpected constraint?