Hi ,

I have a many to many relation ship between two table say a and b. Many to many relation ship is by an association table say a_b.
I am using hibernate annotations(Version 3.2)
Please find below the mapping,SQL to create table

package com.test;

import java.util.Collection;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;


@Entity
@Table(name="a")
public class A {
@Id
@Column(name="a_id")
int id;

@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER)
@JoinTable(name="a_b",joinColumns = @JoinColumn(name="a_key"),inverseJoinColumns= @JoinColumn(name="b_key"))
Collection <B> b;

public int getId() {
return id;
}

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

public Collection<B> getB() {
return b;
}

public void setB(Collection<B> b) {
this.b = b;
}

}



package com.test;

import java.util.Collection;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;


@Entity
@Table(name="b")
public class B {
@Id
@Column(name="b_id")
int id;

@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER)
@JoinTable(name="a_b",joinColumns = @JoinColumn (name="b_key"),inverseJoinColumns = @JoinColumn(name="a_key"))
Collection <A> a;

public int getId() {
return id;
}

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

public Collection<A> getA() {
return a;
}

public void setA(Collection<A> a) {
this.a = a;
}

}

Following are the SQL's to create the table

create table a (
a_id integer primary key
);

create table b (
b_id integer primary key
);

create table map (
a_key integer REFERENCES a(a_id),

b_key integer REFERENCES b(b_id)
);


Lets say a is mapped to 3 entities in b. So the content of the table will be

select * from a;
A_id
----
1


select * from b;
b_id
----
1
2
3

select * from a_b;

a_key b_key
----- -----
1 1
1 2
1 3


Now if i want to save a entity of A, with only one mapping , then it deletes the already existing mapping.

I.e..,

List <B> bs = new ArrayList<B>();
B b1 = new B();
b1.setId(4);
bs.add(b);

A a = new A();
a.setId(1);
a.setB(bs);



session.saveOrUpdate(a);

so it delete above mentioned 3 relations and insert only the newely defined 4th relations.


Hibernate: select a_.a_id from a a_ where a_.a_id=?
Hibernate: delete from map where a_key=?
Hibernate: insert into map (a_key, b_key) values (?, ?)


now when see the content of table a_b i get following

select * from a_b;
a_key b_key
----- -----
1 4


So my question , is there any way to retaint the older relation and add a new as above?

What you are seeing is expected since you are creating a new list that only contains the B with id=4.

You'll have to do something like this instead (with your original code commented out):