Spring Boot: ManyToOne relation with @JoinColumn keeps the foreign key null

Question

followed the same approach for creating oneToMany & ManyToOne relation mapping.

Even though used the @JoinColumn in owning side entity, as per "baeldung" example in the "email entity" but it keeps the foreign key as null.

When I used the @JoinColumn in parent entity i.e. as per in above example in "Employee" entity, then it worked.

but what's the reason behind this behavior of relation mapping ? why this example approach is incorrect ?

Here is my code repo link : https://github.com/TamtePrathamesh/sb_mapping between 'User' & 'mobile' while keeping oneToMany/ManyToOne mapping the mobile table not maintaining the foreign key the entry comes as "NULL". Mobile Mapping Table

I don't think the problem you are having is very clear. Maybe you could show us how you mapped the our entities, and the exact error you are having? — Davide D'Alto, Apr 03 '21 at 21:22
I have attached the code repo link can you please check the code. — Prathamesh Tamte, Apr 04 '21 at 05:49
In github code example 'mobile' entity not maintaining the ManyToOne relation it always inserts NULL in foreign key column — Prathamesh Tamte, Apr 04 '21 at 05:51
You need to show in the question the entities and how you are saving the entity `mobile` in the db. Are you updating the association in both entities? `mobile.user = user` and `user.mobiles.add(mobile)` — Davide D'Alto, Apr 04 '21 at 09:51
https://stackoverflow.com/questions/20068742/jpa-updating-bidirectional-association — Davide D'Alto, Apr 04 '21 at 09:53

Davide D'Alto · Answer 1 · 2021-05-08T17:09:19.427

2

When dealing with a bidirectional association you need to update the association on both sides:

Mobile mobile = ...
User user = ...
user.mobiles.add(mobile);
mobile.user = user;

save(user);

edited May 08 '21 at 17:09

answered Apr 04 '21 at 09:55

Davide D'Alto

1 Answers1