Configure many-to-many relationships in Spring Data REST so deleting one object does not delete the other

Question

I am using the latest Spring Data REST (with JPA and MySQL DB) project. I have two objects that I want to setup a relationship between. But when I delete one of the two, I only want to delete the relationship and the object that received the delete request (not both objects).

What I'm relating:

• A task
• A user

where a task can be related to ("owned by") multiple users and a user can be related to ("own") multiple tasks

Task Class:

@ManyToMany
@JoinTable(name = "task_user", joinColumns = @JoinColumn(name = "task_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "user_id", referencedColumnName = "id"))
private Set<User> users;

User class:

@ManyToMany(mappedBy = "users")
private Set<Task> tasks;

The task_user table consists of two columns

• task_id (the id of the task)
• user_id (the id of the user)

When I delete a task (via DELETE to /task/{id}), it behaves correctly (the task is deleted from the task table and the relationship is deleted from the task_user table). The issue I have is that when I delete a user, it is deleted from the user table but the relationship still exists in the task_user table.

What I desire:

• Deleting a task, deletes all corresponding entries in "task_user" and the entry in "task"; does NOT delete entries in "user"
• Deleting a user, deletes all corresponding entries in "task_user" and the entry in "user"; does not delete entries in "task"

Is it possible to achieve that through configuration? Or do I need to use either foreign keys or custom logic, such as event handlers?

Answer 1

Try this:

public class User {
   //...
   @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
   private Set<Task> tasks;
   //...
}

public class Task {
   //...
    @ManyToMany(mappedBy = "tasks")
    private Set<User> users;
   //...
}

You chose a bidirectional variant of many-to-many so don't forget about 'helper methods' in User class. See documentation: associations many-to-many.

See my example and tests.