Hibernate ManyToMany cascade saving objects

Question

I am trying to understand the principles of ManyToMany relations in Hibernate. I've created a small test project and the question is: I want "Managers" to be saving in db when the "User" is saving. So Manager entity is dependent on User. When I am saving user1 - everything is fine. I am getting user1 and manager1 and manager3 saved to db. But on the next row where I am trying to save user2 to db I am getting an Exception: Converting org.hibernate.PersistentObjectException to JPA PersistenceException : detached entity passed to persist: ua.testing.entities.Manager

I think the problem is because I am trying to save user2 which contains manager1, which was saved in db in previous row. But how can I avoid this problem and make everything work?

User entity:

    package ua.testing.entities;
    
    import jakarta.persistence.*;
    
    import java.util.ArrayList;
    import java.util.List;
    
    @Entity
    @Table(name = "user")
    public class User {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;
        @ManyToMany(cascade = CascadeType.ALL)
        private List<Manager> managerList = new ArrayList<>();
    
        public Long getId() {
            return id;
        }
    
        public void setId(Long id) {
            this.id = id;
        }
    
        public List<Manager> getManagerList() {
            return managerList;
        }
    
        public void setManagerList(List<Manager> managerList) {
            this.managerList = managerList;
        }
    }

Manager entity:

package ua.testing.entities;

import jakarta.persistence.*;

import java.util.ArrayList;
import java.util.List;

@Entity
@Table(name = "manager")
public class Manager {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @ManyToMany(mappedBy = "managerList")
    private List<User> userList = new ArrayList<>();

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public List<User> getUserList() {
        return userList;
    }

    public void setUserList(List<User> userList) {
        this.userList = userList;
    }
}

Main method:

package ua.testing;

import ua.testing.dao.UserDao;
import ua.testing.entities.*;

public class App 
{
    public static void main( String[] args )
    {
        User user1 = new User();
        User user2 = new User();
        User user3 = new User();

        Manager manager1 = new Manager();
        Manager manager2 = new Manager();
        Manager manager3 = new Manager();

        manager1.getUserList().add(user1);
        manager1.getUserList().add(user2);
        manager2.getUserList().add(user1);
        manager2.getUserList().add(user3);
        manager3.getUserList().add(user2);
        manager3.getUserList().add(user3);

        user1.getManagerList().add(manager1);
        user1.getManagerList().add(manager3);
        user2.getManagerList().add(manager1);
        user2.getManagerList().add(manager2);
        user3.getManagerList().add(manager2);
        user3.getManagerList().add(manager3);

        UserDao userDao = new UserDao();
        userDao.persist(user1);
        userDao.persist(user2);  // EXCEPTION HERE

    }

}

Exception I am getting:

Exception in thread "main" jakarta.persistence.PersistenceException: Converting `org.hibernate.PersistentObjectException` to JPA `PersistenceException` : detached entity passed to persist: ua.testing.entities.Manager
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:165)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:175)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:182)
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:783)
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:725)
    at org.hibernate.engine.spi.CascadingActions$7.cascade(CascadingActions.java:299)
    at org.hibernate.engine.spi.CascadingActions$7.cascade(CascadingActions.java:289)
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:511)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:432)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:218)
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:545)
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:475)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:435)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:218)
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:151)
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:474)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:298)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:192)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:122)
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:184)
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:129)
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:53)
    at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:107)
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:735)
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:719)
    at ua.testing.dao.UserDao.persist(UserDao.java:13)
    at ua.testing.App.main(App.java:34)
Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: ua.testing.entities.Manager
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:121)
    at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:118)
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:777)
    ... 23 more