JPA Hibertane unidirectional one-to-one with shared primary key save parent first NO REVERSE

I'v been searching internet for answer, but nothing was working for me. There is a lot of topics with similar cases but specific details are different in a way that make them unusable for me.

So I have two tables: t_item and t_item_info:

item_id field from t_item_info table references id field from t_item table. I'm using mysql db and id column form t_item is auto incremented

I need to make unidirectional one-to-one mapping in a specific way. Here are my classes:

@Entity
@Table(name = "t_item")
public class Item {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false)
    @PrimaryKeyJoinColumn(name = "id", referencedColumnName = "item_id")
    private ItemInfo info;
}

And other one

@Entity
@Table(name = "t_item_info")
public class ItemInfo {
    @Id
    private Long itemId;

    private String descr;
}

So the point is that i need Item object to have a reference to ItemInfo object. NOT The other way!

Item -> ItemInfo   --YES
Item <- ItemInfo   --NO

The other thing is that i need parent (Item) id to become id for a child (ItemInfo)

For example I create Item object with null id and set it's info field with ItemInfo object which also have null id field. Like this:

{
  "id": null,
  "name": "Some name",
  "info": {
    "itemId": null,
    "descr": "some descr"
  }
}

Then when Item object persists hibernate should generate id for parent(Item) object and set it as itemId field for child(ItemInfo).

I have been trying to achieve this with different hibernate annotations and I noticed that no matter how hard I tried Hibernate always seems to try to persist child object first. I noticed it in the logs when I turned sql logging on. insert into t_item_info always goes first (and dies because of null id :D)

So the question is: Is it even possible to achieve this and if so what should I change in my code to do so

I hope that what I'm trying to ask makes sens to you given my poor explanations =)

Why people always insist the child object table in one-to-one associations should be the one with the foreign key is beyond me.

Anyway, as a workaround, since both objects share the id and the association is non-optional, you might as well declare the autogenerated key for the child object:

@Entity
@Table(name = "t_item_info")
public class ItemInfo {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long itemId;

    private String descr;
}

and then use @MapsId for the parent:

@Entity
@Table(name = "t_item")
public class Item {
    @Id
    private Long id;

    private String name;

    @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "id")
    @MapsId
    private ItemInfo info;
}

Note that this approach, will, in a sense, fool Hibernate into thinking it is the Item that should be treated as the child object. You have been warned.

While there is an accepted answer here it looks to me like @Secondary table would be a better and more convenient solution: you may have 2 tables at the database level but I do not see any reason that that fact needs be exposed to any client code. There does not seem to be a lot of benefit to that? The following gives you a simpler API.

Entity:

@Entity
@Table(name = "t_item")
@SecondaryTable("t_item_info",  pkJoinColumns={
        @PrimaryKeyJoinColumn(name="id", referencedColumnName="item_id")})
public class Item {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @Colulumn(name = "description", table= "t_item_info"")
    private String description;
}

API:

{
  "id": null,
  "name": "Some name",
  "descr": "some descr"
}