Hi,
I have defined a many to many relationship between two classes, viz.
Event and Person (defined in a separate database table person_event).
The code of these classes is listed at the end. Now, suppose I want to
delete a person, so all its related associations with events must also
get deleted from the person_event table. In other words, I want cascade
ON DELETE.
Lets consider a scenario.
- The "events" table contains three events identified by id=1, 2, 3.
- The "person" table contains two persons identified by id=4, 5.
- The "person_event' table containing associations like 1-4, 2-4, 3-5
Now, suppose I delete event 1 using Hibernate.delete(), then not only
does it delete event1, and association person_event1-4, but also the
person4 and subsequently, person_event2-4 and event2.
I dont understand why this is happening. Could someone please explain
where I am committing a mistake.
Thanks in advance
- Abhishek
Event and Person Class
package test;
import java.io.Serializable;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
@Entity
@Table(name="events")
public class Event implements Serializable {
private Long id;
private String title;
private Date date;
public Event() {
}
@Id @GeneratedValue(strategy=GenerationType.AUTO)
public Long getId() {
return id;
}
private void setId(Long id) {
this.id = id;
}
@Temporal(TemporalType.TIMESTAMP)
public Date getDate() {
return date;
}
public void setDate(Date date) {
this.date = date;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
private Set<Person> participants = new HashSet<Person>();
@ManyToMany(
cascade={CascadeType.ALL},
mappedBy="events",
targetEntity=Person.class
)
public Set<Person> getParticipants() {
return participants;
}
public void setParticipants(Set<Person> participants) {
this.participants = participants;
}
}
package test;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Entity
@Table(name="person")
public class Person implements Serializable {
private Long person_id;
private int age;
private String firstname;
private String lastname;
public Person() {}
@Id @GeneratedValue(strategy=GenerationType.AUTO)
public Long getId() {
return person_id;
}
public void setId(Long id) {
this.person_id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getFirstname() {
return firstname;
}
public void setFirstname(String firstname) {
this.firstname = firstname;
}
public String getLastname() {
return lastname;
}
public void setLastname(String lastname) {
this.lastname = lastname;
}
private Set<Event> events = new HashSet<Event>();
@ManyToMany(
targetEntity=Event.class,
cascade={CascadeType.ALL}
)
@JoinTable(
name="person_event",
joinColumns={@JoinColumn(name="person_id")},
inverseJoinColumns={@JoinColumn(name="event_id")})
// Defensive, convenience methods
protected Set<Event> getEvents() {
return events;
}
protected void setEvents(Set<Event> events) {
this.events = events;
}
public void addToEvent(Event event) {
this.getEvents().add(event);
event.getParticipants().add(this);
}
public void removeFromEvent(Event event) {
this.getEvents().remove(event);
event.getParticipants().remove(this);
}
}
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