How to remove entity with ManyToMany relationship in JPA and corresponding join table rows

Question

Let s say I have two entities  Group and User  Every user can be member of many groups and every group can have many users    Entity public class User        ManyToMany     Set lt Group gt  groups                Entity public class Group        ManyToMany mappedBy  groups       Set lt User gt  users                Now I want to remove a group  let s say it has many members    Problem is that when I call EntityManager remove   on some Group  JPA provider  in my case Hibernate  does not remove rows from join table and delete operation fails due to foreign key constrains  Calling remove   on User works fine  I guess this has something to do with owning side of relationship    So how can I remove a group in this case    Only way I could come up with is to load all users in the group  then for every user remove current group from his groups and update user  But it seems ridiculous to me to call update   on every user from the group just to be able to delete this group

User · Answer

This is a good solution  The best part is on the SQL side     fine tuning to any level is easy   I used MySql and MySql Workbench to Cascade on delete for the Required Foreign KEY   ALTER TABLE schema joined table  ADD CONSTRAINT UniqueKey FOREIGN KEY  key2  REFERENCES schema table1  id  ON DELETE CASCADE

User · Answer

For my case  I deleted the mappedBy and joined tables like this     ManyToMany cascade   CascadeType ALL   JoinTable name    user group   joinColumns              JoinColumn name    user   referencedColumnName    user id      inverseJoinColumns              JoinColumn name    group   referencedColumnName    group id      private List lt User gt  users    ManyToMany cascade   CascadeType ALL  fetch   FetchType EAGER   JsonIgnore private List lt Group gt  groups

User · Answer

This works for me on a similar issue where I failed to delete the user due to the reference  Thank you    ManyToMany cascade    CascadeType MERGE  CascadeType PERSIST CascadeType REFRESH

User · Answer

For what its worth  I am using EclipseLink  2 3 2 v20111125-r10461 and if I have a  ManyToMany unidirectional relationship I observe the problem that you describe  However  if I change it to be a bi-directional  ManyToMany relationship I am able to delete an entity from the non-owning side and the JOIN table is updated appropriately  This is all without the use of any cascade attributes

User · Answer

I found a possible solution  but    I don t know if it s a good solution    Entity public class Role extends Identifiable         ManyToMany cascade   CascadeType MERGE  CascadeType PERSIST  CascadeType REFRESH        JoinTable name  Role Permission               joinColumns  JoinColumn name  Role id                inverseJoinColumns  JoinColumn name  Permission id                 public List lt Permission gt  getPermissions             return permissions             public void setPermissions List lt Permission gt  permissions            this permissions   permissions            Entity public class Permission extends Identifiable         ManyToMany cascade    CascadeType MERGE  CascadeType PERSIST  CascadeType REFRESH        JoinTable name  Role Permission               joinColumns  JoinColumn name  Permission id                inverseJoinColumns  JoinColumn name  Role id                 public List lt Role gt  getRoles             return roles             public void setRoles List lt Role gt  roles            this roles   roles          I have tried this and it works  When you delete Role  also the relations are deleted  but not the Permission entities  and when you delete Permission  the relations with Role are deleted too  but not the Role instance   But we are mapping a unidirectional relation two times and both entities are the owner of the relation  Could this cause some problems to Hibernate  Which type of problems   Thanks   The code above is from another post related

User · Answer

The following works for me  Add the following method to the entity that is not the owner of the relationship  Group    PreRemove private void removeGroupsFromUsers         for  User u   users            u getGroups   remove this             Keep in mind that for this to work  the Group must have an updated list of Users  which is not done automatically   so everytime you add a Group to the group list in User entity  you should also add a User to the user list in the Group entity

User · Answer

As an alternative to JPA Hibernate solutions   you could use a CASCADE DELETE clause in the database definition of your foregin key on your join table  such as  Oracle syntax     CONSTRAINT fk to group      FOREIGN KEY  group id       REFERENCES group  id       ON DELETE CASCADE   That way the DBMS itself automatically deletes the row that points to the group when you delete the group  And it works whether the delete is made from Hibernate JPA  JDBC  manually in the DB or any other way   the cascade delete feature is supported by all major DBMS  Oracle  MySQL  SQL Server  PostgreSQL

User · Answer

This works for me    Transactional public void remove Integer groupId        Group group   groupRepository findOne groupId       group getUsers   removeAll group getUsers             Other business logic      groupRepository delete group       Also  mark the method  Transactional  org springframework transaction annotation Transactional   this will do whole process in one session  saves some time

User · Answer

The ownership of the relation is determined by where you place the  mappedBy  attribute to the annotation  The entity you put  mappedBy  is the one which is NOT the owner  There s no chance for both sides to be owners  If you don t have a  delete user  use-case you could simply move the ownership to the Group entity  as currently the User is the owner  On the other hand  you haven t been asking about it  but one thing worth to know  The groups and users are not combined with each other  I mean  after deleting User1 instance from Group1 users  the User1 groups collections is not changed automatically  which is quite surprising for me   All in all  I would suggest you decide who is the owner  Let say the User is the owner  Then when deleting a user the relation user-group will be updated automatically  But when deleting a group you have to take care of deleting the relation yourself like this      entityManager remove group  for  User user   group users         user groups remove group            then merge   and flush

User · Answer

This is what I ended up doing  Hopefully someone might find it useful   Transactional public void deleteGroup Long groupId        Group group   groupRepository findById groupId  orElseThrow        group getUsers   forEach u - gt  u getGroups   remove group        userRepository saveAll group getUsers         groupRepository delete group

[java] How to remove entity with ManyToMany relationship in JPA (and corresponding join table rows)?

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