There is a problem with deleting many to many association - postgresql

Question

#entity
#table(name = "users")
public class User {
#Id
private Long id;
private String name;
#ManyToMany(cascade = {PERSIST, MERGE})
#JoinTable(name = "user_following",
joinColumns = {#JoinColumn(name = "user_id")},
inverseJoinColumns = {#JoinColumn(name = "user_following_id")})
private List<User> following;
#ManyToMany(cascade = {PERSIST, MERGE})
#JoinTable(name = "user_followers",
joinColumns = {#JoinColumn(name = "user_id")},
inverseJoinColumns = {#JoinColumn(name = "user_follower_id")})
private List<User> followers;
//some other fields, getters and setters
public void follow(User user) {
following.add(user);
user.acceptFollower(this);
}
public void acceptFollower(User user) {
followers.add(user);
}
}
We have three tables:
users
user_following
user_followers
Imagine having this entity and you are implementing following & followers functionality.
We have to users - rick & tom.
User rick = new User(1, "rick");
User tom = new User(2, "tom");
rick.follow(tom);
After calling method - rick.follow(tom);
We will populate our tables in the following way
Table - "users"
id
name
1
rick
2
tom
Table - "user_following"
user_id
user_following_id
1
2
Table - "user_followers"
user_id
user_follower_id
2
1
So far, everything works just great but the problem starts when i try to delete users.
For example:
userRepository.deleteById(1)
JPA gives an error -
update or delete on table "users" violates foreign key constraint "fk1yg7xqw2kfx6n2196o0gr3obc" on table "user_followers"
Подробности: Key (id)=(1) is still referenced from table "user_followers".
JPA cannot delete because it generates a wrong sql.
Hibernate:
select
user0_.id as id1_5_,
user0_.first_name as first_na5_5_,
from
users user0_
where
user0_.username=?
Hibernate:
delete
from
user_followers
where
user_id=?
Hibernate:
delete
from
user_following
where
user_id=?
Hibernate:
delete
from
users
where
id=?
I want to delete user - rick whose id = 1
The error happens due to wrong sql.
When we delete user - 'rick',
we first delete 'rick' from "user_following" and "user_followers" tables.
Look at the this statement.
Hibernate:
delete
from
user_followers
where
user_id=?
The error happens due to this statement because the
user we are deleting corresponds to the (user_following_id) column of the "user_followers" table,
not "user_id" column.
The right sql statement must be:
Hibernate:
delete
from
user_followers
where
user_following_id=?
Is there a way how to fix this?

Answer 1

Do not create user_followers as a table, instead create it as a view on the table user_following. The view definition merely reverses the column names. I do not know your obscurification manager so I will just supply the needed SQL. (see demo).
create table users( id integer primary key
, name text
) ;
create table user_following( user_id integer
references users(id)
on delete cascade
, user_following_id integer
references users(id)
on delete cascade
, constraint user_following_pk
primary key (user_id,user_following_id)
) ;
create view user_followers as
select user_following_id as user_id
, user_id as user_follower_id
from user_following;